The Microsoft file server remote VSS protocol (MS-FSRVP) allows a file server client to use a shadow copy-aware utility (like the Microsoft DiskShadow utility) to create a point-in-time copy of one or more SMB shares hosted on a NAS server (a shadow copy set). A shadow copy-aware backup utility can use the shadow copy to back up the state of an application that hosts its data on a NAS server. If necessary, the shadow copy can later be used to restore the application state.
Internally, the NAS server uses file cloning to produce the shadow copies. Because it may take some time to produce a copy, the MS-FSRVP protocol is generally used to copy a share containing a small number of large files (less than 10,000) rather than a large number of small files. Shares used to host virtual machine configuration files and disks are often backed up using the MS-FSRVP protocol.
In order to use the Microsoft file server remote VSS protocol to back up a group of SMB shares, you must ensure that:
- The client connecting to the NAS server and the NAS server EVS hosting the share must have SMB3 support enabled. SMB3 support is enabled on a per-EVS basis on the NAS server. To find out the maximum SMB version is supported by a particular EVS, use the cifs-max-supported-version command.
- The path of the share to be backed up may not be just the root path of the share (\); the path of the share to be backed up must include a named path (something like \anything). You can use the command cifs-share list to display the path of a share.
- The share to be part of a shadow copy set must have at least one plain file or directory under the path root.
- The share to be part of a shadow copy set must contain only directories and plain files. The share must not contain files with hard links, external cross-volume links (XVLs), or files that have been migrated, ingested, or virtualized.
You can use the commands virtualization-path-list and migration-list-paths to check for migration and virtualization paths.
- By default, the total number of files and directories of a shadow copy set to be committed must be 10000 or less. You can change this maximum using the NAS server set fsrvp_maxcloneable command.
- The user issuing the FSRVP protocol request must be a member of the NAS server's local "Backup Operators" group.
The DiskShadow utility typically uses the machine account name to connect to the NAS server when using the FSRVP protocol. Therefore, the machine account of the client must be added to the NAS server's "localgroup," and the machine account name must end with a $ character. To list and add accounts to the Backup Operators group, use the NAS server command localgroup.
- No share in a shadow copy set may include a subdirectory that is mapped to another share (an overlaying path).
To check for overlaying paths, use the NAS server command cifs-share list to examine all the shares.
- A share should not be actively in use when a VSS snapshot is taken. We recommend that the clients using the share should be quiesced before the snapshot is taken.
A NAS server administrator can exclude a share from a shadow copy set by using the cifs-share mod --shadow-copy-use disable <share_name> command to disallow the share from being in a shadow copy set.