Difference between revisions of "Server-Side Copy"

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'''Limitations'''
 
'''Limitations'''
 
* The client's FSCTL_SRV_COPYCHUNK server-side copy request must be Btrfs filesystem aligned
 
* The client's FSCTL_SRV_COPYCHUNK server-side copy request must be Btrfs filesystem aligned
** Otherwise, Samba falls back to a [https://wiki.samba.org/index.php/Server-Side_Copy#Server-Side_Copy_offload regular server-side copy]
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** Otherwise, Samba falls back to a [https://wiki.samba.org/index.php/Server-Side_Copy#Server-Side_Copy_Offload regular server-side copy]
  
  

Revision as of 14:49, 13 November 2013

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

Sequence

  1. Client issues read requests to server
  2. Server reads file data off disk
  3. Server sends data to client
  4. Client sends duplicate file data to server
  5. Server writes duplicate file data to disk


Result

  • File data traverses network and disk
  • Duplicate file data stored on disk


Server-Side Copy Offload

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

Sequence

  1. Client issues FSCTL_SRV_COPYCHUNK requests to server
  2. Server reads file data off disk
  3. Server writes duplicate file data to disk


Result

  • File data traverses disk only
    • Network round trip avoided
  • Duplicate file data stored on disk

Samba's smbd file server supports SMB2 Copy-Chunk requests by default, no additional configuration is required.


Btrfs Enhanced Server-Side Copy Offload

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

Sequence

  1. Client issues FSCTL_SRV_COPYCHUNK requests to server
  2. Server issues BTRFS_IOC_CLONE_RANGE filesystem ioctl


Result

  • File data does not traverse network or disk
    • Filesystem meta-data update only
  • No duplication of file data
    • Source and destination files share the same on disk data extents

Btrfs enhanced server-side copy can be enabled in smb.conf on a per share basis with:

   [share]
   path = /mnt/btrfs_fs/        # must reside within a Btrfs filesystem
   vfs objects = btrfs

Limitations

  • The client's FSCTL_SRV_COPYCHUNK server-side copy request must be Btrfs filesystem aligned


Client Support

Windows Server 2012, Windows 8, and later releases support SMB2 FSCTL_SRV_COPYCHUNK server-side copy operations. On these platforms, Windows explorer initiated file copies attempt server-side copy offload by default. Preliminary patches have been proposed for the Linux Kernel CIFS client. Server-side copy offload is initiated on Linux using cp --reflink.