[Storage]Fix sync copy small blob fail #15548 (#15557)

Author: blueww

src/Storage/Storage.Management/ChangeLog.md

@@ -27,6 +27,8 @@
     -  `Get-AzStorageBlobQueryResult`
 * Made `Get-AzDataLakeGen2ChildItem` list all datalake gen2 items by default, instead of needing user to list chunk by chunk.
 * Fixed BlobProperties is empty issue when using sas without prefix '?' [#15460]
+* Fixed synchronously copy small blob failure [#15548]
+    - `Copy-AzStorageBlob`
 
 ## Version 3.9.0
 * Supported enable/disable Blob container soft delete

src/Storage/Storage/Blob/StorageDataMovementCmdletBase.cs

@@ -27,6 +27,8 @@ public class StorageDataMovementCmdletBase : StorageCloudBlobCmdletBase, IDispos
     {
         protected const int size4MB = 4 * 1024 * 1024;
 
+        protected const int size8MB = 8 * 1024 * 1024;
+
         /// <summary>
         /// block blob type
         /// </summary>
@@ -178,12 +180,16 @@ protected virtual void DoEndProcessing()
         /// </summary>
         public static long GetBlockLength(long contentLength)
         {
+            if (contentLength <= size8MB)
+            {
+                return contentLength;
+            }
             long blockLength = contentLength / 50000;
-            if (blockLength % (8 * 1024 * 1024) != 0)
+            if (blockLength % (size8MB) != 0)
             {
-                blockLength = (blockLength / (8 * 1024 * 1024) + 1) * (8 * 1024 * 1024);
+                blockLength = (blockLength / (size8MB) + 1) * (size8MB);
             }
-            return blockLength;
+            return blockLength > 0 ? blockLength : contentLength;
         }
 
         /// <summary>