Using SAN hardware snapshots

If your VMware vSphere uses a storage area network (SAN) storage system as a datastore, you can enable Agent for VMware (Windows) to use SAN hardware snapshots when performing a backup.

Why use SAN hardware snapshots?

Agent for VMware needs a virtual machine snapshot in order to create a consistent backup. Because the agent reads the virtual disk content from the snapshot, the snapshot must be kept for the whole duration of the backup process.

By default, the agent uses native VMware snapshots created by the ESXi host. While the snapshot is kept, the virtual disk files are in the read-only state, and the host writes all changes done to the disks to separate delta files. Once the backup process is finished, the host deletes the snapshot, i.e. merges the delta files with the virtual disk files.

Both maintaining and deleting the snapshot affect the virtual machine performance. With large virtual disks and fast data changes, these operations take a long time during which the performance can degrade. In extreme cases, when several machines are backed up simultaneously, the growing delta files may nearly fill the datastore and cause all of the virtual machines to power off.

You can reduce the hypervisor resource utilization by offloading the snapshots to the SAN. In this case, the sequence of operations is as follows:

1. The ESXi takes a VMware snapshot in the beginning of the backup process, to bring the virtual disks to a consistent state.
2. The SAN creates a hardware snapshot of the volume or LUN that contains the virtual machine and its VMware snapshot. This operation typically takes a few seconds.
3. The ESXi deletes the VMware snapshot. Agent for VMware reads the virtual disk content from the SAN hardware snapshot.

Because the VMware snapshot is maintained only for a few seconds, the virtual machine performance degradation is minimized.

What do I need to use the SAN hardware snapshots?

If you want to use the SAN hardware snapshots when backing up virtual machines, ensure that all of the following is true:

• The NetApp SAN storage meets the requirements described in "NetApp SAN storage requirements".
• The machine running Agent for VMware (Windows) is configured as described in "Configuring the machine running Agent for VMware".
• The SAN storage is registered on the management server.
• [If there are Agents for VMware that did not take part in the above registration] The virtual machines that reside on the SAN storage are assigned to the SAN-enabled agents, as described in "Virtual machine binding".
• The "SAN hardware snapshots" backup option is enabled in the protection plan options.