Friday, August 19, 2016

PernixData Backup Best Practices - 4. SAN Backup Mode

To close this backup best practices series we end with the SAN Backup Mode. In SAN Backup Mode the storage device where the VMs actually is running from, is mounted to the backup server to bypass the ESXi environment altogether. The backup then takes place via the storage protocol (Fibre Channel,iSCSI, etc.) locally on the backup server. While this is a very performant way of doing backups it has some dependencies on the backup process itself. The following figure illustrates how the SAN Backup Mode works.
Screen Shot 2016-06-06 at 17.06.31.png
Figure 1: SAN Backup Mode

  1. Backup triggers the backup in most cases talking to vCenter or the ESXi as well as the storage system.
  2. If required, it is possible to quiesce the I/O of the VMs to make the backup crash-consistent.
  3. Call to the Storage System to create a Snapshot of the existing Device (LUN).
  4. Backup Server mounts the Device (LUN) in Read-Only mode
  5. Backup Server then backups the VMDKs which belong to the VM.

From the FVP perspective when VMs are in Write-Through mode this works as expected since the SAN always has the latest data. In Write-Back mode while the SAN Snapshot has been created, FVP might still hold some data blocks within the acceleration layer which have not yet been destaged to the SAN, therefore some data on the SAN might be outdated. To ensure that backups obtained while VM(s) is/are in WB mode, are consistent, an integration of FVP with the backup software is required, typically achieved via scripts. A list of scrips can be found here: FVP Powershell Tools.

The Powershell commandlets are installed on the PernixData Management Host in case Windows is in use or it can be installed on a separate host using the Windows installation binaries and choose custom installation while then choosing the PowerShell integration.


  1. What about product Storage Snapshot technologies like NetApp SMVI over NFS ?

  2. For sure you can do that and we wrote an integration for this. Please have a look at: there you find a PowerShell Script: backup-netapp-vsc.ps1