Server-Side Copy

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Introduction

Samba 4.1.0 was the first release to ship with support for server-side copy operations via the SMB2 FSCTL_SRV_COPYCHUNK request. Clients making use of server-side copy support, such as Windows Server 2012, can experience considerable performance improvements for file copy operations, as file data need not traverse the network. This feature is enabled by default on the smbd file server.


Traditional File Copy

Prior to Samba 4.1.0, clients traditionally copied files by reading the source file data over the network and writing it back to the server through to the destination file on disk.

Traditional copy.png

  * Client issues read requests to server
  * Server reads file data off disk
  * Server sends data to client
  * Client sends duplicate file data to server
  * Server writes duplicate file data to disk


Server-Side Copy

With Samba 4.1.0 and later, clients can offload copy operations to the server using Copy-Chunk requests. In processing such a request, the network round-trip is avoided.

Serverside copy.png

  * Client issues FSCTL_SRV_COPYCHUNK requests to server
  * Server reads file data off disk
  * Server writes duplicate file data to disk


Btrfs Enhanced Server-Side Copy

Along with server-side copy support, a Btrfs specific Samba VFS Module was newly added with 4.1.0. This module improves the performance and efficiency of server-side copy operations on Btrfs backed shares, by using the Btrfs clone-range IOCTL.

Btrfs serverside copy.png

  * Client issues FSCTL_SRV_COPYCHUNK requests to server
  * Server issues BTRFS_IOC_CLONE_RANGE filesystem ioctl