diff --git a/pkg/filemanager/driver/local/local.go b/pkg/filemanager/driver/local/local.go
index 172effb8..33f6ea93 100644
--- a/pkg/filemanager/driver/local/local.go
+++ b/pkg/filemanager/driver/local/local.go
@@ -226,6 +226,12 @@ func (handler *Driver) Token(ctx context.Context, uploadSession *fs.UploadSessio
 		if err := Fallocate(f, 0, uploadSession.Props.Size); err != nil {
 			handler.l.Warning("Failed to preallocate file: %s", err)
 		}
+	} else {
+		// When disk pre-allocation is disabled, concurrent chunk uploads must be 1
+		// to avoid disk fragmentation and write contention on local storage.
+ 		settings := *handler.Policy.Settings
+ 		settings.ChunkConcurrency = 1
+ 		handler.Policy.Settings = &settings
 	}
 
 	return &fs.UploadCredential{
diff --git a/pkg/filemanager/driver/remote/remote.go b/pkg/filemanager/driver/remote/remote.go
index 42b2b1af..cc0b89fa 100644
--- a/pkg/filemanager/driver/remote/remote.go
+++ b/pkg/filemanager/driver/remote/remote.go
@@ -150,6 +150,14 @@ func (handler *Driver) Token(ctx context.Context, uploadSession *fs.UploadSessio
 		return nil, fmt.Errorf("failed to sign upload url: %w", err)
 	}
 
+	// When disk pre-allocation is disabled, concurrent chunk uploads must be 1
+	// to avoid disk fragmentation and write contention on slave storage.
+	if !handler.Policy.Settings.PreAllocate {
+		settings := *handler.Policy.Settings
+		settings.ChunkConcurrency = 1
+		handler.Policy.Settings = &settings
+	}
+
 	return &fs.UploadCredential{
 		SessionID:  uploadSession.Props.UploadSessionID,
 		ChunkSize:  handler.Policy.Settings.ChunkSize,