azureblob: add --azureblob-disable-checksum flag

backend/azureblob/azureblob.go

@@ -125,6 +125,16 @@ If blobs are in "archive tier" at remote, trying to perform data transfer
 operations from remote will not be allowed. User should first restore by
 tiering blob to "Hot" or "Cool".`,
 			Advanced: true,
+		}, {
+			Name: "disable_checksum",
+			Help: `Don't store MD5 checksum with object metadata.
+
+Normally rclone will calculate the MD5 checksum of the input before
+uploading it so it can add it to metadata on the object. This is great
+for data integrity checking but can cause long delays for large files
+to start uploading.`,
+			Default:  false,
+			Advanced: true,
 		}, {
 			Name:     config.ConfigEncoding,
 			Help:     config.ConfigEncodingHelp,
@@ -150,6 +160,7 @@ type Options struct {
 	ListChunkSize   uint                 `config:"list_chunk"`
 	AccessTier      string               `config:"access_tier"`
 	UseEmulator     bool                 `config:"use_emulator"`
+	DisableCheckSum bool                 `config:"disable_checksum"`
 	Enc             encoder.MultiEncoder `config:"encoding"`
 }
 
@@ -1395,6 +1406,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 	// will be set in PutBlockList API call using the 'x-ms-blob-content-md5' header
 	// Note: If multipart, a MD5 checksum will also be computed for each uploaded block
 	// 		 in order to validate its integrity during transport
+	if !o.fs.opt.DisableCheckSum {
 		if sourceMD5, _ := src.Hash(ctx, hash.MD5); sourceMD5 != "" {
 			sourceMD5bytes, err := hex.DecodeString(sourceMD5)
 			if err == nil {
@@ -1403,6 +1415,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 				fs.Debugf(o, "Failed to decode %q as MD5: %v", sourceMD5, err)
 			}
 		}
+	}
 
 	putBlobOptions := azblob.UploadStreamToBlockBlobOptions{
 		BufferSize:      int(o.fs.opt.ChunkSize),