Expert Says, January 2015: FreeNAS 9.3 Features – Support for VMware VAAI

With all the excitement over the big changes introduced in FreeNAS 9.3 (including the new update manager and the decision to completely move to ZFS), it’s easy to overlook some of the other features that were added during the release. One of those features we’d like to highlight was the added support for coherent VMware snapshots so ZFS snapshots and VMware snapshots are properly coordinated.

iXsystems worked with FreeBSD developers to add additional VMware VAAI primitives to the iSCSI protocol in FreeBSD. This feature was then brought over to FreeNAS and as a result, FreeNAS 9.3 now fully supports the following VAAI block and thin provisioning primitives:

• Write Same Zero – Repetitive write operations are performed by FreeNAS
• Xcopy (Full Copy) – FreeNAS will mass copy blocks
• Atomic Test and Set – FreeNAS does not lock a full LUN allowing other VMs on that LUN
to run
• UNMAP – A thin provisioning API that ensures that FreeNAS never uses more space
than needed
• Warn & Stun – Another thin provisioning operation that ensures that VMs don’t encounter
an out-of-space condition or crash. You can address the out-of-space issue in FreeNAS
and then restart affected VMs.

Also, FreeNAS tells VMware that it is thinly provisioned and will create ZFS snapshots to replace the VMware snapshots.

These features enable FreeNAS to integrate better with VMware deployments. These changes will also be implemented in an upcoming TrueNAS release, making it easier for our customers to use TrueNAS to back virtualization environments.

For more information about VAAI, check out the VMware site.


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