From cc53525c9df66e3ba46eab234ed2df56f122ce54 Mon Sep 17 00:00:00 2001
From: tanyasethi-msft <tanyasethi@microsoft.com>
Date: Mon, 25 May 2026 16:26:29 +0530
Subject: [PATCH 1/7] [Storage] Change default parallelism to CPU-based value
 across azblob, azfile, azdatalake

Update default concurrency for uploads and downloads from a fixed value
of 5 (or 1 for stream uploads) to Clamp(NumCPU, 8, 96), matching the
Rust SDK implementation. This improves throughput on modern multi-core
VMs while clamping prevents resource exhaustion on small or very large
machines.

Adds AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true env var opt-out
to revert to the previous default of 5.
---
 sdk/storage/azblob/blob/constants.go          |  9 +++-
 sdk/storage/azblob/blob/models.go             |  9 ++--
 .../azblob/blockblob/chunkwriting_test.go     |  2 +-
 sdk/storage/azblob/blockblob/models.go        |  8 +--
 .../azblob/internal/shared/batch_transfer.go  | 17 +++++-
 .../azblob/internal/shared/shared_test.go     | 43 +++++++++++++++
 sdk/storage/azdatalake/file/models.go         | 14 +++--
 .../internal/shared/batch_transfer.go         | 21 +++++++-
 .../internal/shared/batch_transfer_test.go    | 53 +++++++++++++++++++
 sdk/storage/azfile/file/models.go             | 17 +++---
 .../azfile/internal/shared/batch_transfer.go  | 21 +++++++-
 .../internal/shared/batch_transfer_test.go    | 53 +++++++++++++++++++
 12 files changed, 245 insertions(+), 22 deletions(-)
 create mode 100644 sdk/storage/azdatalake/internal/shared/batch_transfer_test.go
 create mode 100644 sdk/storage/azfile/internal/shared/batch_transfer_test.go

diff --git a/sdk/storage/azblob/blob/constants.go b/sdk/storage/azblob/blob/constants.go
index ef47450b5ea6..6a3f45bcdec6 100644
--- a/sdk/storage/azblob/blob/constants.go
+++ b/sdk/storage/azblob/blob/constants.go
@@ -17,10 +17,17 @@ const (
 	// DefaultDownloadBlockSize is default block size
 	DefaultDownloadBlockSize = int64(4 * 1024 * 1024) // 4MB
 
-	// DefaultConcurrency is the default number of blocks downloaded or uploaded in parallel
+	// DefaultConcurrency is the legacy default number of blocks downloaded or uploaded in parallel.
+	// Deprecated: Use DefaultConcurrencyValue() instead, which returns a value based on CPU core count.
 	DefaultConcurrency = shared.DefaultConcurrency
 )
 
+// DefaultConcurrencyValue returns the default concurrency for parallel uploads/downloads.
+// The value is based on CPU core count, clamped between 8 and 96.
+func DefaultConcurrencyValue() uint16 {
+	return shared.DefaultConcurrencyValue()
+}
+
 // BlobType defines values for BlobType
 type BlobType = generated.BlobType
 
diff --git a/sdk/storage/azblob/blob/models.go b/sdk/storage/azblob/blob/models.go
index 9acec4594fb3..3ecac8bff373 100644
--- a/sdk/storage/azblob/blob/models.go
+++ b/sdk/storage/azblob/blob/models.go
@@ -122,7 +122,8 @@ type downloadOptions struct {
 	CPKInfo      *CPKInfo
 	CPKScopeInfo *CPKScopeInfo
 
-	// Concurrency indicates the maximum number of blocks to download in parallel (0=default).
+	// Concurrency indicates the maximum number of blocks to download in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 
 	// RetryReaderOptionsPerBlock is used when downloading each block.
@@ -176,7 +177,8 @@ type DownloadBufferOptions struct {
 	// CPKScopeInfo contains a group of parameters for client provided encryption scope.
 	CPKScopeInfo *CPKScopeInfo
 
-	// Concurrency indicates the maximum number of blocks to download in parallel (0=default).
+	// Concurrency indicates the maximum number of blocks to download in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 
 	// RetryReaderOptionsPerBlock is used when downloading each block.
@@ -204,7 +206,8 @@ type DownloadFileOptions struct {
 	CPKInfo      *CPKInfo
 	CPKScopeInfo *CPKScopeInfo
 
-	// Concurrency indicates the maximum number of blocks to download in parallel.  The default value is 5.
+	// Concurrency indicates the maximum number of blocks to download in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 
 	// RetryReaderOptionsPerBlock is used when downloading each block.
diff --git a/sdk/storage/azblob/blockblob/chunkwriting_test.go b/sdk/storage/azblob/blockblob/chunkwriting_test.go
index d8f5473ebde1..ed6ee6e90961 100644
--- a/sdk/storage/azblob/blockblob/chunkwriting_test.go
+++ b/sdk/storage/azblob/blockblob/chunkwriting_test.go
@@ -177,7 +177,7 @@ func TestSlowDestCopyFrom(t *testing.T) {
 		require.ErrorIs(t, err, io.ErrNoProgress)
 	}
 
-	require.Equal(t, 1, tracker.Count)
+	require.GreaterOrEqual(t, tracker.Count, 1)
 	require.True(t, tracker.Freed)
 }
 
diff --git a/sdk/storage/azblob/blockblob/models.go b/sdk/storage/azblob/blockblob/models.go
index 868637ffc481..09799c5b8446 100644
--- a/sdk/storage/azblob/blockblob/models.go
+++ b/sdk/storage/azblob/blockblob/models.go
@@ -273,7 +273,8 @@ type uploadFromReaderOptions struct {
 	CPKInfo      *blob.CPKInfo
 	CPKScopeInfo *blob.CPKScopeInfo
 
-	// Concurrency indicates the maximum number of blocks to upload in parallel (0=default)
+	// Concurrency indicates the maximum number of blocks to upload in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 
 	TransactionalValidation blob.TransferValidationType
@@ -334,7 +335,8 @@ type UploadStreamOptions struct {
 	BlockSize int64
 
 	// Concurrency defines the max number of concurrent uploads to be performed to upload the file.
-	// Each concurrent upload will create a buffer of size BlockSize.  The default value is one.
+	// Each concurrent upload will create a buffer of size BlockSize.  The default is based on
+	// CPU core count (min 8, max 96).
 	Concurrency int
 
 	TransactionalValidation blob.TransferValidationType
@@ -350,7 +352,7 @@ type UploadStreamOptions struct {
 
 func (u *UploadStreamOptions) setDefaults() {
 	if u.Concurrency == 0 {
-		u.Concurrency = 1
+		u.Concurrency = int(shared.DefaultConcurrencyValue())
 	}
 
 	if u.BlockSize < _1MiB {
diff --git a/sdk/storage/azblob/internal/shared/batch_transfer.go b/sdk/storage/azblob/internal/shared/batch_transfer.go
index 7fc26f543d06..95e38fc7ba44 100644
--- a/sdk/storage/azblob/internal/shared/batch_transfer.go
+++ b/sdk/storage/azblob/internal/shared/batch_transfer.go
@@ -6,12 +6,27 @@ package shared
 import (
 	"context"
 	"errors"
+	"os"
+	"runtime"
+	"strings"
 )
 
 const (
+	// DefaultConcurrency is the legacy default concurrency value.
+	// Deprecated: Use DefaultConcurrencyValue() instead, which returns a value based on CPU core count.
 	DefaultConcurrency = 5
 )
 
+// DefaultConcurrencyValue returns the default concurrency based on CPU count,
+// clamped between 8 and 96. Set the AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY
+// environment variable to "true" to revert to the previous default of 5.
+func DefaultConcurrencyValue() uint16 {
+	if strings.EqualFold(os.Getenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY"), "true") {
+		return DefaultConcurrency
+	}
+	return uint16(max(8, min(96, runtime.NumCPU())))
+}
+
 // BatchTransferOptions identifies options used by doBatchTransfer.
 type BatchTransferOptions struct {
 	TransferSize  int64
@@ -30,7 +45,7 @@ func DoBatchTransfer(ctx context.Context, o *BatchTransferOptions) error {
 	}
 
 	if o.Concurrency == 0 {
-		o.Concurrency = DefaultConcurrency // default concurrency
+		o.Concurrency = DefaultConcurrencyValue()
 	}
 
 	// Prepare and do parallel operations.
diff --git a/sdk/storage/azblob/internal/shared/shared_test.go b/sdk/storage/azblob/internal/shared/shared_test.go
index d4cd2c7b2e7a..70be7bf26263 100644
--- a/sdk/storage/azblob/internal/shared/shared_test.go
+++ b/sdk/storage/azblob/internal/shared/shared_test.go
@@ -4,6 +4,7 @@
 package shared
 
 import (
+	"runtime"
 	"strings"
 	"testing"
 
@@ -207,3 +208,45 @@ func TestIsIPEndpointStyle(t *testing.T) {
 	require.True(t, IsIPEndpointStyle("127.0.0.1"))
 	require.True(t, IsIPEndpointStyle("127.0.0.1:80"))
 }
+
+func TestDefaultConcurrencyValue_InBounds(t *testing.T) {
+	val := DefaultConcurrencyValue()
+	require.GreaterOrEqual(t, val, uint16(8))
+	require.LessOrEqual(t, val, uint16(96))
+}
+
+func TestDefaultConcurrencyValue_Deterministic(t *testing.T) {
+	val1 := DefaultConcurrencyValue()
+	val2 := DefaultConcurrencyValue()
+	require.Equal(t, val1, val2)
+}
+
+func TestDefaultConcurrencyValue_MatchesCPU(t *testing.T) {
+	cpus := runtime.NumCPU()
+	val := DefaultConcurrencyValue()
+	if cpus < 8 {
+		require.Equal(t, uint16(8), val)
+	} else if cpus > 96 {
+		require.Equal(t, uint16(96), val)
+	} else {
+		require.Equal(t, uint16(cpus), val)
+	}
+}
+
+func TestDefaultConcurrencyValue_LegacyEnvVar(t *testing.T) {
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "true")
+	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
+
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "TRUE")
+	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
+
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "false")
+	val := DefaultConcurrencyValue()
+	require.GreaterOrEqual(t, val, uint16(8))
+	require.LessOrEqual(t, val, uint16(96))
+
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "")
+	val = DefaultConcurrencyValue()
+	require.GreaterOrEqual(t, val, uint16(8))
+	require.LessOrEqual(t, val, uint16(96))
+}
diff --git a/sdk/storage/azdatalake/file/models.go b/sdk/storage/azdatalake/file/models.go
index 4ff0c58b897a..550eb248f743 100644
--- a/sdk/storage/azdatalake/file/models.go
+++ b/sdk/storage/azdatalake/file/models.go
@@ -141,7 +141,8 @@ type uploadFromReaderOptions struct {
 	// Progress is a function that is invoked periodically as bytes are sent to the FileClient.
 	// Note that the progress reporting is not always increasing; it can go down when retrying a request.
 	Progress func(bytesTransferred int64)
-	// Concurrency indicates the maximum number of chunks to upload in parallel (default is 5)
+	// Concurrency indicates the maximum number of chunks to upload in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 	// AccessConditions contains optional parameters to access leased entity.
 	AccessConditions *AccessConditions
@@ -157,7 +158,8 @@ type uploadFromReaderOptions struct {
 type UploadStreamOptions struct {
 	// ChunkSize specifies the chunk size to use in bytes; the default (and maximum size) is MaxAppendBytes.
 	ChunkSize int64
-	// Concurrency indicates the maximum number of chunks to upload in parallel (default is 5)
+	// Concurrency indicates the maximum number of chunks to upload in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 	// AccessConditions contains optional parameters to access leased entity.
 	AccessConditions *AccessConditions
@@ -324,7 +326,7 @@ func (o *AppendDataOptions) format(offset int64, body io.ReadSeekCloser) (*gener
 
 func (u *UploadStreamOptions) setDefaults() {
 	if u.Concurrency == 0 {
-		u.Concurrency = 1
+		u.Concurrency = shared.DefaultConcurrencyValue()
 	}
 
 	if u.ChunkSize < _1MiB {
@@ -428,7 +430,8 @@ type DownloadBufferOptions struct {
 	CPKInfo *CPKInfo
 	// CPKScopeInfo contains a group of parameters for client provided encryption scope.
 	CPKScopeInfo *CPKScopeInfo
-	// Concurrency indicates the maximum number of chunks to download in parallel (0=default).
+	// Concurrency indicates the maximum number of chunks to download in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
 	RetryReaderOptionsPerChunk *RetryReaderOptions
@@ -482,7 +485,8 @@ type DownloadFileOptions struct {
 	CPKInfo *CPKInfo
 	// CPKScopeInfo contains a group of parameters for client provided encryption scope.
 	CPKScopeInfo *CPKScopeInfo
-	// Concurrency indicates the maximum number of chunks to download in parallel. The default value is 5.
+	// Concurrency indicates the maximum number of chunks to download in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
 	RetryReaderOptionsPerChunk *RetryReaderOptions
diff --git a/sdk/storage/azdatalake/internal/shared/batch_transfer.go b/sdk/storage/azdatalake/internal/shared/batch_transfer.go
index 2c5cf54c07c9..1aa30a8868bf 100644
--- a/sdk/storage/azdatalake/internal/shared/batch_transfer.go
+++ b/sdk/storage/azdatalake/internal/shared/batch_transfer.go
@@ -6,8 +6,27 @@ package shared
 import (
 	"context"
 	"errors"
+	"os"
+	"runtime"
+	"strings"
 )
 
+const (
+	// DefaultConcurrency is the legacy default concurrency value.
+	// Deprecated: Use DefaultConcurrencyValue() instead, which returns a value based on CPU core count.
+	DefaultConcurrency = 5
+)
+
+// DefaultConcurrencyValue returns the default concurrency based on CPU count,
+// clamped between 8 and 96. Set the AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY
+// environment variable to "true" to revert to the previous default of 5.
+func DefaultConcurrencyValue() uint16 {
+	if strings.EqualFold(os.Getenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY"), "true") {
+		return DefaultConcurrency
+	}
+	return uint16(max(8, min(96, runtime.NumCPU())))
+}
+
 // BatchTransferOptions identifies options used by doBatchTransfer.
 type BatchTransferOptions struct {
 	TransferSize  int64
@@ -25,7 +44,7 @@ func DoBatchTransfer(ctx context.Context, o *BatchTransferOptions) error {
 	}
 
 	if o.Concurrency == 0 {
-		o.Concurrency = 5 // default concurrency
+		o.Concurrency = DefaultConcurrencyValue()
 	}
 
 	// Prepare and do parallel operations.
diff --git a/sdk/storage/azdatalake/internal/shared/batch_transfer_test.go b/sdk/storage/azdatalake/internal/shared/batch_transfer_test.go
new file mode 100644
index 000000000000..20bbfbefbc71
--- /dev/null
+++ b/sdk/storage/azdatalake/internal/shared/batch_transfer_test.go
@@ -0,0 +1,53 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+package shared
+
+import (
+	"runtime"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestDefaultConcurrencyValue_InBounds(t *testing.T) {
+	val := DefaultConcurrencyValue()
+	require.GreaterOrEqual(t, val, uint16(8))
+	require.LessOrEqual(t, val, uint16(96))
+}
+
+func TestDefaultConcurrencyValue_Deterministic(t *testing.T) {
+	val1 := DefaultConcurrencyValue()
+	val2 := DefaultConcurrencyValue()
+	require.Equal(t, val1, val2)
+}
+
+func TestDefaultConcurrencyValue_MatchesCPU(t *testing.T) {
+	cpus := runtime.NumCPU()
+	val := DefaultConcurrencyValue()
+	if cpus < 8 {
+		require.Equal(t, uint16(8), val)
+	} else if cpus > 96 {
+		require.Equal(t, uint16(96), val)
+	} else {
+		require.Equal(t, uint16(cpus), val)
+	}
+}
+
+func TestDefaultConcurrencyValue_LegacyEnvVar(t *testing.T) {
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "true")
+	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
+
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "TRUE")
+	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
+
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "false")
+	val := DefaultConcurrencyValue()
+	require.GreaterOrEqual(t, val, uint16(8))
+	require.LessOrEqual(t, val, uint16(96))
+
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "")
+	val = DefaultConcurrencyValue()
+	require.GreaterOrEqual(t, val, uint16(8))
+	require.LessOrEqual(t, val, uint16(96))
+}
diff --git a/sdk/storage/azfile/file/models.go b/sdk/storage/azfile/file/models.go
index 0dd5122c1556..1cb8c8496cd7 100644
--- a/sdk/storage/azfile/file/models.go
+++ b/sdk/storage/azfile/file/models.go
@@ -606,7 +606,8 @@ type downloadOptions struct {
 	// LeaseAccessConditions contains optional parameters to access leased entity.
 	LeaseAccessConditions *LeaseAccessConditions
 
-	// Concurrency indicates the maximum number of chunks to download in parallel (0=default).
+	// Concurrency indicates the maximum number of chunks to download in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
@@ -646,7 +647,8 @@ type DownloadBufferOptions struct {
 	// LeaseAccessConditions contains optional parameters to access leased entity.
 	LeaseAccessConditions *LeaseAccessConditions
 
-	// Concurrency indicates the maximum number of chunks to download in parallel (0=default).
+	// Concurrency indicates the maximum number of chunks to download in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
@@ -669,7 +671,8 @@ type DownloadFileOptions struct {
 	// LeaseAccessConditions contains optional parameters to access leased entity.
 	LeaseAccessConditions *LeaseAccessConditions
 
-	// Concurrency indicates the maximum number of chunks to download in parallel (0=default).
+	// Concurrency indicates the maximum number of chunks to download in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
@@ -1050,7 +1053,8 @@ type uploadFromReaderOptions struct {
 	// Note that the progress reporting is not always increasing; it can go down when retrying a request.
 	Progress func(bytesTransferred int64)
 
-	// Concurrency indicates the maximum number of chunks to upload in parallel (default is 5)
+	// Concurrency indicates the maximum number of chunks to upload in parallel.
+	// The default is based on CPU core count (min 8, max 96).
 	Concurrency uint16
 
 	// LeaseAccessConditions contains optional parameters to access leased entity.
@@ -1078,7 +1082,8 @@ type UploadStreamOptions struct {
 	ChunkSize int64
 
 	// Concurrency defines the max number of concurrent uploads to be performed to upload the file.
-	// Each concurrent upload will create a buffer of size ChunkSize.  The default value is one.
+	// Each concurrent upload will create a buffer of size ChunkSize.  The default is based on
+	// CPU core count (min 8, max 96).
 	Concurrency int
 
 	// LeaseAccessConditions contains optional parameters to access leased entity.
@@ -1087,7 +1092,7 @@ type UploadStreamOptions struct {
 
 func (u *UploadStreamOptions) setDefaults() {
 	if u.Concurrency == 0 {
-		u.Concurrency = 1
+		u.Concurrency = int(shared.DefaultConcurrencyValue())
 	}
 
 	if u.ChunkSize < _1MiB {
diff --git a/sdk/storage/azfile/internal/shared/batch_transfer.go b/sdk/storage/azfile/internal/shared/batch_transfer.go
index 2c5cf54c07c9..1aa30a8868bf 100644
--- a/sdk/storage/azfile/internal/shared/batch_transfer.go
+++ b/sdk/storage/azfile/internal/shared/batch_transfer.go
@@ -6,8 +6,27 @@ package shared
 import (
 	"context"
 	"errors"
+	"os"
+	"runtime"
+	"strings"
 )
 
+const (
+	// DefaultConcurrency is the legacy default concurrency value.
+	// Deprecated: Use DefaultConcurrencyValue() instead, which returns a value based on CPU core count.
+	DefaultConcurrency = 5
+)
+
+// DefaultConcurrencyValue returns the default concurrency based on CPU count,
+// clamped between 8 and 96. Set the AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY
+// environment variable to "true" to revert to the previous default of 5.
+func DefaultConcurrencyValue() uint16 {
+	if strings.EqualFold(os.Getenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY"), "true") {
+		return DefaultConcurrency
+	}
+	return uint16(max(8, min(96, runtime.NumCPU())))
+}
+
 // BatchTransferOptions identifies options used by doBatchTransfer.
 type BatchTransferOptions struct {
 	TransferSize  int64
@@ -25,7 +44,7 @@ func DoBatchTransfer(ctx context.Context, o *BatchTransferOptions) error {
 	}
 
 	if o.Concurrency == 0 {
-		o.Concurrency = 5 // default concurrency
+		o.Concurrency = DefaultConcurrencyValue()
 	}
 
 	// Prepare and do parallel operations.
diff --git a/sdk/storage/azfile/internal/shared/batch_transfer_test.go b/sdk/storage/azfile/internal/shared/batch_transfer_test.go
new file mode 100644
index 000000000000..20bbfbefbc71
--- /dev/null
+++ b/sdk/storage/azfile/internal/shared/batch_transfer_test.go
@@ -0,0 +1,53 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+package shared
+
+import (
+	"runtime"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestDefaultConcurrencyValue_InBounds(t *testing.T) {
+	val := DefaultConcurrencyValue()
+	require.GreaterOrEqual(t, val, uint16(8))
+	require.LessOrEqual(t, val, uint16(96))
+}
+
+func TestDefaultConcurrencyValue_Deterministic(t *testing.T) {
+	val1 := DefaultConcurrencyValue()
+	val2 := DefaultConcurrencyValue()
+	require.Equal(t, val1, val2)
+}
+
+func TestDefaultConcurrencyValue_MatchesCPU(t *testing.T) {
+	cpus := runtime.NumCPU()
+	val := DefaultConcurrencyValue()
+	if cpus < 8 {
+		require.Equal(t, uint16(8), val)
+	} else if cpus > 96 {
+		require.Equal(t, uint16(96), val)
+	} else {
+		require.Equal(t, uint16(cpus), val)
+	}
+}
+
+func TestDefaultConcurrencyValue_LegacyEnvVar(t *testing.T) {
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "true")
+	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
+
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "TRUE")
+	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
+
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "false")
+	val := DefaultConcurrencyValue()
+	require.GreaterOrEqual(t, val, uint16(8))
+	require.LessOrEqual(t, val, uint16(96))
+
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "")
+	val = DefaultConcurrencyValue()
+	require.GreaterOrEqual(t, val, uint16(8))
+	require.LessOrEqual(t, val, uint16(96))
+}

From 43cd16f985d097477a09975796b4b242b038991f Mon Sep 17 00:00:00 2001
From: tanyasethi-msft <tanyasethi@microsoft.com>
Date: Mon, 25 May 2026 17:55:15 +0530
Subject: [PATCH 2/7] Add GiB-scale parallelism benchmarks for upload/download
 buffer and stream

---
 .../blockblob/parallelism_bench_test.go       | 142 ++++++++++++++++++
 1 file changed, 142 insertions(+)
 create mode 100644 sdk/storage/azblob/blockblob/parallelism_bench_test.go

diff --git a/sdk/storage/azblob/blockblob/parallelism_bench_test.go b/sdk/storage/azblob/blockblob/parallelism_bench_test.go
new file mode 100644
index 000000000000..780300cb6a67
--- /dev/null
+++ b/sdk/storage/azblob/blockblob/parallelism_bench_test.go
@@ -0,0 +1,142 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+package blockblob_test
+
+import (
+	"bytes"
+	"context"
+	"crypto/rand"
+	"fmt"
+	"testing"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blob"
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blockblob"
+)
+
+// GiB-scale parallelism benchmarks to measure the impact of default concurrency changes.
+// These use UploadBuffer/DownloadBuffer which perform parallel chunked transfers,
+// where concurrency directly affects throughput.
+//
+// Run with:
+//   AZURE_STORAGE_ACCOUNT_NAME=... AZURE_STORAGE_ACCOUNT_KEY=... \
+//   go test ./blockblob/... -bench 'BenchmarkParallelism' -benchtime=3x -run '^$' -timeout 1800s
+//
+// To compare old vs new defaults:
+//   # Old default (concurrency=5):
+//   AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true go test ...
+//   # New default (concurrency=NumCPU clamped 8-96):
+//   go test ...
+
+func BenchmarkParallelismUploadBuffer(b *testing.B) {
+	sizes := []struct {
+		name string
+		size int
+	}{
+		{"256MB", 256 * 1024 * 1024},
+		{"512MB", 512 * 1024 * 1024},
+		{"1GiB", 1024 * 1024 * 1024},
+		{"2GiB", 2 * 1024 * 1024 * 1024},
+		{"4GiB", 4 * 1024 * 1024 * 1024},
+	}
+
+	for _, sz := range sizes {
+		b.Run(sz.name, func(b *testing.B) {
+			data := make([]byte, sz.size)
+			_, _ = rand.Read(data)
+
+			env := setupBenchEnv(b)
+			b.SetBytes(int64(sz.size))
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				blobName := fmt.Sprintf("par-upbuf-%s-%d", sz.name, i)
+				bbClient := env.containerClient.NewBlockBlobClient(blobName)
+				_, err := bbClient.UploadBuffer(context.Background(), data, &blockblob.UploadBufferOptions{})
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+	}
+}
+
+func BenchmarkParallelismUploadStream(b *testing.B) {
+	sizes := []struct {
+		name string
+		size int
+	}{
+		{"256MB", 256 * 1024 * 1024},
+		{"512MB", 512 * 1024 * 1024},
+		{"1GiB", 1024 * 1024 * 1024},
+		{"2GiB", 2 * 1024 * 1024 * 1024},
+		{"4GiB", 4 * 1024 * 1024 * 1024},
+	}
+
+	for _, sz := range sizes {
+		b.Run(sz.name, func(b *testing.B) {
+			data := make([]byte, sz.size)
+			_, _ = rand.Read(data)
+
+			env := setupBenchEnv(b)
+			b.SetBytes(int64(sz.size))
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				blobName := fmt.Sprintf("par-upstr-%s-%d", sz.name, i)
+				bbClient := env.containerClient.NewBlockBlobClient(blobName)
+				_, err := bbClient.UploadStream(context.Background(),
+					bytes.NewReader(data),
+					&blockblob.UploadStreamOptions{})
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+	}
+}
+
+func BenchmarkParallelismDownloadBuffer(b *testing.B) {
+	sizes := []struct {
+		name string
+		size int
+	}{
+		{"256MB", 256 * 1024 * 1024},
+		{"512MB", 512 * 1024 * 1024},
+		{"1GiB", 1024 * 1024 * 1024},
+		{"2GiB", 2 * 1024 * 1024 * 1024},
+		{"4GiB", 4 * 1024 * 1024 * 1024},
+	}
+
+	for _, sz := range sizes {
+		b.Run(sz.name, func(b *testing.B) {
+			data := make([]byte, sz.size)
+			_, _ = rand.Read(data)
+
+			env := setupBenchEnv(b)
+
+			// Upload the blob once before benchmarking download
+			blobName := fmt.Sprintf("par-dlbuf-%s", sz.name)
+			bbClient := env.containerClient.NewBlockBlobClient(blobName)
+			_, err := bbClient.UploadBuffer(context.Background(), data, nil)
+			if err != nil {
+				b.Fatal(err)
+			}
+
+			// Get blob properties to know the size for buffer allocation
+			props, err := bbClient.GetProperties(context.Background(), nil)
+			if err != nil {
+				b.Fatal(err)
+			}
+			blobSize := *props.ContentLength
+
+			b.SetBytes(blobSize)
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				buf := make([]byte, blobSize)
+				_, err := bbClient.BlobClient().DownloadBuffer(context.Background(), buf, &blob.DownloadBufferOptions{})
+				if err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+	}
+}

From f35f22ea371ecdd2a11b7666c64051b68275893f Mon Sep 17 00:00:00 2001
From: tanyasethi-msft <tanyasethi@microsoft.com>
Date: Mon, 25 May 2026 18:03:50 +0530
Subject: [PATCH 3/7] Remove duplicate test files from azfile and azdatalake

---
 .../internal/shared/batch_transfer_test.go    | 53 -------------------
 .../internal/shared/batch_transfer_test.go    | 53 -------------------
 2 files changed, 106 deletions(-)
 delete mode 100644 sdk/storage/azdatalake/internal/shared/batch_transfer_test.go
 delete mode 100644 sdk/storage/azfile/internal/shared/batch_transfer_test.go

diff --git a/sdk/storage/azdatalake/internal/shared/batch_transfer_test.go b/sdk/storage/azdatalake/internal/shared/batch_transfer_test.go
deleted file mode 100644
index 20bbfbefbc71..000000000000
--- a/sdk/storage/azdatalake/internal/shared/batch_transfer_test.go
+++ /dev/null
@@ -1,53 +0,0 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
-// Licensed under the MIT License. See License.txt in the project root for license information.
-
-package shared
-
-import (
-	"runtime"
-	"testing"
-
-	"github.com/stretchr/testify/require"
-)
-
-func TestDefaultConcurrencyValue_InBounds(t *testing.T) {
-	val := DefaultConcurrencyValue()
-	require.GreaterOrEqual(t, val, uint16(8))
-	require.LessOrEqual(t, val, uint16(96))
-}
-
-func TestDefaultConcurrencyValue_Deterministic(t *testing.T) {
-	val1 := DefaultConcurrencyValue()
-	val2 := DefaultConcurrencyValue()
-	require.Equal(t, val1, val2)
-}
-
-func TestDefaultConcurrencyValue_MatchesCPU(t *testing.T) {
-	cpus := runtime.NumCPU()
-	val := DefaultConcurrencyValue()
-	if cpus < 8 {
-		require.Equal(t, uint16(8), val)
-	} else if cpus > 96 {
-		require.Equal(t, uint16(96), val)
-	} else {
-		require.Equal(t, uint16(cpus), val)
-	}
-}
-
-func TestDefaultConcurrencyValue_LegacyEnvVar(t *testing.T) {
-	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "true")
-	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
-
-	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "TRUE")
-	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
-
-	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "false")
-	val := DefaultConcurrencyValue()
-	require.GreaterOrEqual(t, val, uint16(8))
-	require.LessOrEqual(t, val, uint16(96))
-
-	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "")
-	val = DefaultConcurrencyValue()
-	require.GreaterOrEqual(t, val, uint16(8))
-	require.LessOrEqual(t, val, uint16(96))
-}
diff --git a/sdk/storage/azfile/internal/shared/batch_transfer_test.go b/sdk/storage/azfile/internal/shared/batch_transfer_test.go
deleted file mode 100644
index 20bbfbefbc71..000000000000
--- a/sdk/storage/azfile/internal/shared/batch_transfer_test.go
+++ /dev/null
@@ -1,53 +0,0 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
-// Licensed under the MIT License. See License.txt in the project root for license information.
-
-package shared
-
-import (
-	"runtime"
-	"testing"
-
-	"github.com/stretchr/testify/require"
-)
-
-func TestDefaultConcurrencyValue_InBounds(t *testing.T) {
-	val := DefaultConcurrencyValue()
-	require.GreaterOrEqual(t, val, uint16(8))
-	require.LessOrEqual(t, val, uint16(96))
-}
-
-func TestDefaultConcurrencyValue_Deterministic(t *testing.T) {
-	val1 := DefaultConcurrencyValue()
-	val2 := DefaultConcurrencyValue()
-	require.Equal(t, val1, val2)
-}
-
-func TestDefaultConcurrencyValue_MatchesCPU(t *testing.T) {
-	cpus := runtime.NumCPU()
-	val := DefaultConcurrencyValue()
-	if cpus < 8 {
-		require.Equal(t, uint16(8), val)
-	} else if cpus > 96 {
-		require.Equal(t, uint16(96), val)
-	} else {
-		require.Equal(t, uint16(cpus), val)
-	}
-}
-
-func TestDefaultConcurrencyValue_LegacyEnvVar(t *testing.T) {
-	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "true")
-	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
-
-	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "TRUE")
-	require.Equal(t, uint16(DefaultConcurrency), DefaultConcurrencyValue())
-
-	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "false")
-	val := DefaultConcurrencyValue()
-	require.GreaterOrEqual(t, val, uint16(8))
-	require.LessOrEqual(t, val, uint16(96))
-
-	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "")
-	val = DefaultConcurrencyValue()
-	require.GreaterOrEqual(t, val, uint16(8))
-	require.LessOrEqual(t, val, uint16(96))
-}

From 0ac90732b8af1d32ae7e6b367300b38f5815ae45 Mon Sep 17 00:00:00 2001
From: tanyasethi-msft <tanyasethi@microsoft.com>
Date: Mon, 25 May 2026 18:04:28 +0530
Subject: [PATCH 4/7] Remove benchmark file from PR

---
 .../blockblob/parallelism_bench_test.go       | 142 ------------------
 1 file changed, 142 deletions(-)
 delete mode 100644 sdk/storage/azblob/blockblob/parallelism_bench_test.go

diff --git a/sdk/storage/azblob/blockblob/parallelism_bench_test.go b/sdk/storage/azblob/blockblob/parallelism_bench_test.go
deleted file mode 100644
index 780300cb6a67..000000000000
--- a/sdk/storage/azblob/blockblob/parallelism_bench_test.go
+++ /dev/null
@@ -1,142 +0,0 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
-// Licensed under the MIT License. See License.txt in the project root for license information.
-
-package blockblob_test
-
-import (
-	"bytes"
-	"context"
-	"crypto/rand"
-	"fmt"
-	"testing"
-
-	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blob"
-	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blockblob"
-)
-
-// GiB-scale parallelism benchmarks to measure the impact of default concurrency changes.
-// These use UploadBuffer/DownloadBuffer which perform parallel chunked transfers,
-// where concurrency directly affects throughput.
-//
-// Run with:
-//   AZURE_STORAGE_ACCOUNT_NAME=... AZURE_STORAGE_ACCOUNT_KEY=... \
-//   go test ./blockblob/... -bench 'BenchmarkParallelism' -benchtime=3x -run '^$' -timeout 1800s
-//
-// To compare old vs new defaults:
-//   # Old default (concurrency=5):
-//   AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true go test ...
-//   # New default (concurrency=NumCPU clamped 8-96):
-//   go test ...
-
-func BenchmarkParallelismUploadBuffer(b *testing.B) {
-	sizes := []struct {
-		name string
-		size int
-	}{
-		{"256MB", 256 * 1024 * 1024},
-		{"512MB", 512 * 1024 * 1024},
-		{"1GiB", 1024 * 1024 * 1024},
-		{"2GiB", 2 * 1024 * 1024 * 1024},
-		{"4GiB", 4 * 1024 * 1024 * 1024},
-	}
-
-	for _, sz := range sizes {
-		b.Run(sz.name, func(b *testing.B) {
-			data := make([]byte, sz.size)
-			_, _ = rand.Read(data)
-
-			env := setupBenchEnv(b)
-			b.SetBytes(int64(sz.size))
-			b.ResetTimer()
-			for i := 0; i < b.N; i++ {
-				blobName := fmt.Sprintf("par-upbuf-%s-%d", sz.name, i)
-				bbClient := env.containerClient.NewBlockBlobClient(blobName)
-				_, err := bbClient.UploadBuffer(context.Background(), data, &blockblob.UploadBufferOptions{})
-				if err != nil {
-					b.Fatal(err)
-				}
-			}
-		})
-	}
-}
-
-func BenchmarkParallelismUploadStream(b *testing.B) {
-	sizes := []struct {
-		name string
-		size int
-	}{
-		{"256MB", 256 * 1024 * 1024},
-		{"512MB", 512 * 1024 * 1024},
-		{"1GiB", 1024 * 1024 * 1024},
-		{"2GiB", 2 * 1024 * 1024 * 1024},
-		{"4GiB", 4 * 1024 * 1024 * 1024},
-	}
-
-	for _, sz := range sizes {
-		b.Run(sz.name, func(b *testing.B) {
-			data := make([]byte, sz.size)
-			_, _ = rand.Read(data)
-
-			env := setupBenchEnv(b)
-			b.SetBytes(int64(sz.size))
-			b.ResetTimer()
-			for i := 0; i < b.N; i++ {
-				blobName := fmt.Sprintf("par-upstr-%s-%d", sz.name, i)
-				bbClient := env.containerClient.NewBlockBlobClient(blobName)
-				_, err := bbClient.UploadStream(context.Background(),
-					bytes.NewReader(data),
-					&blockblob.UploadStreamOptions{})
-				if err != nil {
-					b.Fatal(err)
-				}
-			}
-		})
-	}
-}
-
-func BenchmarkParallelismDownloadBuffer(b *testing.B) {
-	sizes := []struct {
-		name string
-		size int
-	}{
-		{"256MB", 256 * 1024 * 1024},
-		{"512MB", 512 * 1024 * 1024},
-		{"1GiB", 1024 * 1024 * 1024},
-		{"2GiB", 2 * 1024 * 1024 * 1024},
-		{"4GiB", 4 * 1024 * 1024 * 1024},
-	}
-
-	for _, sz := range sizes {
-		b.Run(sz.name, func(b *testing.B) {
-			data := make([]byte, sz.size)
-			_, _ = rand.Read(data)
-
-			env := setupBenchEnv(b)
-
-			// Upload the blob once before benchmarking download
-			blobName := fmt.Sprintf("par-dlbuf-%s", sz.name)
-			bbClient := env.containerClient.NewBlockBlobClient(blobName)
-			_, err := bbClient.UploadBuffer(context.Background(), data, nil)
-			if err != nil {
-				b.Fatal(err)
-			}
-
-			// Get blob properties to know the size for buffer allocation
-			props, err := bbClient.GetProperties(context.Background(), nil)
-			if err != nil {
-				b.Fatal(err)
-			}
-			blobSize := *props.ContentLength
-
-			b.SetBytes(blobSize)
-			b.ResetTimer()
-			for i := 0; i < b.N; i++ {
-				buf := make([]byte, blobSize)
-				_, err := bbClient.BlobClient().DownloadBuffer(context.Background(), buf, &blob.DownloadBufferOptions{})
-				if err != nil {
-					b.Fatal(err)
-				}
-			}
-		})
-	}
-}

From 625689624345af7367c151c60f3dab52b4216b31 Mon Sep 17 00:00:00 2001
From: tanyasethi-msft <tanyasethi@microsoft.com>
Date: Mon, 25 May 2026 18:15:37 +0530
Subject: [PATCH 5/7] Address review comments: hermetic tests and env var in
 doc comments

---
 sdk/storage/azblob/blob/constants.go              |  1 +
 sdk/storage/azblob/blob/models.go                 |  6 +++---
 sdk/storage/azblob/blockblob/models.go            |  4 ++--
 sdk/storage/azblob/internal/shared/shared_test.go |  3 +++
 sdk/storage/azdatalake/file/models.go             |  8 ++++----
 sdk/storage/azfile/file/models.go                 | 10 +++++-----
 6 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/sdk/storage/azblob/blob/constants.go b/sdk/storage/azblob/blob/constants.go
index 6a3f45bcdec6..918d587b38c8 100644
--- a/sdk/storage/azblob/blob/constants.go
+++ b/sdk/storage/azblob/blob/constants.go
@@ -24,6 +24,7 @@ const (
 
 // DefaultConcurrencyValue returns the default concurrency for parallel uploads/downloads.
 // The value is based on CPU core count, clamped between 8 and 96.
+// Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default of 5.
 func DefaultConcurrencyValue() uint16 {
 	return shared.DefaultConcurrencyValue()
 }
diff --git a/sdk/storage/azblob/blob/models.go b/sdk/storage/azblob/blob/models.go
index 3ecac8bff373..a23329c19f70 100644
--- a/sdk/storage/azblob/blob/models.go
+++ b/sdk/storage/azblob/blob/models.go
@@ -123,7 +123,7 @@ type downloadOptions struct {
 	CPKScopeInfo *CPKScopeInfo
 
 	// Concurrency indicates the maximum number of blocks to download in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 
 	// RetryReaderOptionsPerBlock is used when downloading each block.
@@ -178,7 +178,7 @@ type DownloadBufferOptions struct {
 	CPKScopeInfo *CPKScopeInfo
 
 	// Concurrency indicates the maximum number of blocks to download in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 
 	// RetryReaderOptionsPerBlock is used when downloading each block.
@@ -207,7 +207,7 @@ type DownloadFileOptions struct {
 	CPKScopeInfo *CPKScopeInfo
 
 	// Concurrency indicates the maximum number of blocks to download in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 
 	// RetryReaderOptionsPerBlock is used when downloading each block.
diff --git a/sdk/storage/azblob/blockblob/models.go b/sdk/storage/azblob/blockblob/models.go
index 09799c5b8446..4e3bac2863f8 100644
--- a/sdk/storage/azblob/blockblob/models.go
+++ b/sdk/storage/azblob/blockblob/models.go
@@ -274,7 +274,7 @@ type uploadFromReaderOptions struct {
 	CPKScopeInfo *blob.CPKScopeInfo
 
 	// Concurrency indicates the maximum number of blocks to upload in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 
 	TransactionalValidation blob.TransferValidationType
@@ -336,7 +336,7 @@ type UploadStreamOptions struct {
 
 	// Concurrency defines the max number of concurrent uploads to be performed to upload the file.
 	// Each concurrent upload will create a buffer of size BlockSize.  The default is based on
-	// CPU core count (min 8, max 96).
+	// CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency int
 
 	TransactionalValidation blob.TransferValidationType
diff --git a/sdk/storage/azblob/internal/shared/shared_test.go b/sdk/storage/azblob/internal/shared/shared_test.go
index 70be7bf26263..e9eafee8699e 100644
--- a/sdk/storage/azblob/internal/shared/shared_test.go
+++ b/sdk/storage/azblob/internal/shared/shared_test.go
@@ -210,18 +210,21 @@ func TestIsIPEndpointStyle(t *testing.T) {
 }
 
 func TestDefaultConcurrencyValue_InBounds(t *testing.T) {
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "")
 	val := DefaultConcurrencyValue()
 	require.GreaterOrEqual(t, val, uint16(8))
 	require.LessOrEqual(t, val, uint16(96))
 }
 
 func TestDefaultConcurrencyValue_Deterministic(t *testing.T) {
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "")
 	val1 := DefaultConcurrencyValue()
 	val2 := DefaultConcurrencyValue()
 	require.Equal(t, val1, val2)
 }
 
 func TestDefaultConcurrencyValue_MatchesCPU(t *testing.T) {
+	t.Setenv("AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY", "")
 	cpus := runtime.NumCPU()
 	val := DefaultConcurrencyValue()
 	if cpus < 8 {
diff --git a/sdk/storage/azdatalake/file/models.go b/sdk/storage/azdatalake/file/models.go
index 550eb248f743..5d8857888af3 100644
--- a/sdk/storage/azdatalake/file/models.go
+++ b/sdk/storage/azdatalake/file/models.go
@@ -142,7 +142,7 @@ type uploadFromReaderOptions struct {
 	// Note that the progress reporting is not always increasing; it can go down when retrying a request.
 	Progress func(bytesTransferred int64)
 	// Concurrency indicates the maximum number of chunks to upload in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 	// AccessConditions contains optional parameters to access leased entity.
 	AccessConditions *AccessConditions
@@ -159,7 +159,7 @@ type UploadStreamOptions struct {
 	// ChunkSize specifies the chunk size to use in bytes; the default (and maximum size) is MaxAppendBytes.
 	ChunkSize int64
 	// Concurrency indicates the maximum number of chunks to upload in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 	// AccessConditions contains optional parameters to access leased entity.
 	AccessConditions *AccessConditions
@@ -431,7 +431,7 @@ type DownloadBufferOptions struct {
 	// CPKScopeInfo contains a group of parameters for client provided encryption scope.
 	CPKScopeInfo *CPKScopeInfo
 	// Concurrency indicates the maximum number of chunks to download in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
 	RetryReaderOptionsPerChunk *RetryReaderOptions
@@ -486,7 +486,7 @@ type DownloadFileOptions struct {
 	// CPKScopeInfo contains a group of parameters for client provided encryption scope.
 	CPKScopeInfo *CPKScopeInfo
 	// Concurrency indicates the maximum number of chunks to download in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
 	RetryReaderOptionsPerChunk *RetryReaderOptions
diff --git a/sdk/storage/azfile/file/models.go b/sdk/storage/azfile/file/models.go
index 1cb8c8496cd7..bfdce6de2de1 100644
--- a/sdk/storage/azfile/file/models.go
+++ b/sdk/storage/azfile/file/models.go
@@ -607,7 +607,7 @@ type downloadOptions struct {
 	LeaseAccessConditions *LeaseAccessConditions
 
 	// Concurrency indicates the maximum number of chunks to download in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
@@ -648,7 +648,7 @@ type DownloadBufferOptions struct {
 	LeaseAccessConditions *LeaseAccessConditions
 
 	// Concurrency indicates the maximum number of chunks to download in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
@@ -672,7 +672,7 @@ type DownloadFileOptions struct {
 	LeaseAccessConditions *LeaseAccessConditions
 
 	// Concurrency indicates the maximum number of chunks to download in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 
 	// RetryReaderOptionsPerChunk is used when downloading each chunk.
@@ -1054,7 +1054,7 @@ type uploadFromReaderOptions struct {
 	Progress func(bytesTransferred int64)
 
 	// Concurrency indicates the maximum number of chunks to upload in parallel.
-	// The default is based on CPU core count (min 8, max 96).
+	// The default is based on CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency uint16
 
 	// LeaseAccessConditions contains optional parameters to access leased entity.
@@ -1083,7 +1083,7 @@ type UploadStreamOptions struct {
 
 	// Concurrency defines the max number of concurrent uploads to be performed to upload the file.
 	// Each concurrent upload will create a buffer of size ChunkSize.  The default is based on
-	// CPU core count (min 8, max 96).
+	// CPU core count (min 8, max 96). Set AZURE_STORAGE_USE_LEGACY_DEFAULT_CONCURRENCY=true to revert to the previous default.
 	Concurrency int
 
 	// LeaseAccessConditions contains optional parameters to access leased entity.

From 236bfd899e43726b714cf84faa3964a204727886 Mon Sep 17 00:00:00 2001
From: tanyasethi-msft <tanyasethi@microsoft.com>
Date: Mon, 25 May 2026 18:28:22 +0530
Subject: [PATCH 6/7] Fix gocritic deprecatedComment: separate Deprecated
 notice into its own paragraph

---
 sdk/storage/azblob/blob/constants.go                     | 1 +
 sdk/storage/azblob/internal/shared/batch_transfer.go     | 1 +
 sdk/storage/azdatalake/internal/shared/batch_transfer.go | 1 +
 sdk/storage/azfile/internal/shared/batch_transfer.go     | 1 +
 4 files changed, 4 insertions(+)

diff --git a/sdk/storage/azblob/blob/constants.go b/sdk/storage/azblob/blob/constants.go
index 918d587b38c8..c00a2019467f 100644
--- a/sdk/storage/azblob/blob/constants.go
+++ b/sdk/storage/azblob/blob/constants.go
@@ -18,6 +18,7 @@ const (
 	DefaultDownloadBlockSize = int64(4 * 1024 * 1024) // 4MB
 
 	// DefaultConcurrency is the legacy default number of blocks downloaded or uploaded in parallel.
+	//
 	// Deprecated: Use DefaultConcurrencyValue() instead, which returns a value based on CPU core count.
 	DefaultConcurrency = shared.DefaultConcurrency
 )
diff --git a/sdk/storage/azblob/internal/shared/batch_transfer.go b/sdk/storage/azblob/internal/shared/batch_transfer.go
index 95e38fc7ba44..e6cc0a03039e 100644
--- a/sdk/storage/azblob/internal/shared/batch_transfer.go
+++ b/sdk/storage/azblob/internal/shared/batch_transfer.go
@@ -13,6 +13,7 @@ import (
 
 const (
 	// DefaultConcurrency is the legacy default concurrency value.
+	//
 	// Deprecated: Use DefaultConcurrencyValue() instead, which returns a value based on CPU core count.
 	DefaultConcurrency = 5
 )
diff --git a/sdk/storage/azdatalake/internal/shared/batch_transfer.go b/sdk/storage/azdatalake/internal/shared/batch_transfer.go
index 1aa30a8868bf..98f0239d2005 100644
--- a/sdk/storage/azdatalake/internal/shared/batch_transfer.go
+++ b/sdk/storage/azdatalake/internal/shared/batch_transfer.go
@@ -13,6 +13,7 @@ import (
 
 const (
 	// DefaultConcurrency is the legacy default concurrency value.
+	//
 	// Deprecated: Use DefaultConcurrencyValue() instead, which returns a value based on CPU core count.
 	DefaultConcurrency = 5
 )
diff --git a/sdk/storage/azfile/internal/shared/batch_transfer.go b/sdk/storage/azfile/internal/shared/batch_transfer.go
index 1aa30a8868bf..98f0239d2005 100644
--- a/sdk/storage/azfile/internal/shared/batch_transfer.go
+++ b/sdk/storage/azfile/internal/shared/batch_transfer.go
@@ -13,6 +13,7 @@ import (
 
 const (
 	// DefaultConcurrency is the legacy default concurrency value.
+	//
 	// Deprecated: Use DefaultConcurrencyValue() instead, which returns a value based on CPU core count.
 	DefaultConcurrency = 5
 )

From 18eb0ba8b4c79edfe95860fbe1b45cfef599873d Mon Sep 17 00:00:00 2001
From: tanyasethi-msft <tanyasethi@microsoft.com>
Date: Mon, 25 May 2026 18:38:47 +0530
Subject: [PATCH 7/7] Fix staticcheck SA1019 for deprecated const re-export

---
 sdk/storage/azblob/blob/constants.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sdk/storage/azblob/blob/constants.go b/sdk/storage/azblob/blob/constants.go
index c00a2019467f..956e5163dc09 100644
--- a/sdk/storage/azblob/blob/constants.go
+++ b/sdk/storage/azblob/blob/constants.go
@@ -20,7 +20,7 @@ const (
 	// DefaultConcurrency is the legacy default number of blocks downloaded or uploaded in parallel.
 	//
 	// Deprecated: Use DefaultConcurrencyValue() instead, which returns a value based on CPU core count.
-	DefaultConcurrency = shared.DefaultConcurrency
+	DefaultConcurrency = shared.DefaultConcurrency //nolint:staticcheck // intentional re-export of deprecated const for backward compat
 )
 
 // DefaultConcurrencyValue returns the default concurrency for parallel uploads/downloads.