Shared Storage Requirements for VMHA

Problem

VMHA evacuation behavior depends on the VM's storage type and the shared storage mounts.

Background

VMHA can trigger an evacuation when a compute host is:

• Powered off

• Network isolated (management plane can’t reach the host)

Storage configuration affects whether the evacuated VM preserves data. It can also introduce NFS lock conflicts.

VM storage types

Ephemeral (local instance disk)

• VM disk data lives under /opt/data/instances.

• If /opt/data/instances is on shared storage and mounted on every hypervisor host, VM data is preserved during evacuation.

• If /opt/data/instances is not shared, evacuation may still succeed, but the instance disk data is lost.

Volume-backed (boot from volume)

• VM volumes are mounted under a path like /opt/pf9/data/state/mnt/<id>.

• VM disk data is not stored under /opt/data/instances.

• Whether /opt/data/instances is shared does not affect data retention for volume-backed VMs.

NFS locking (nolock) considerations

If your shared storage backend is NFS, mount options can change failover behavior:

• With nolock, the evacuated VM will start without NFS lock checks.

• Without nolock, the evacuated VM will fail to start if the old VM still holds locks.

nolock disables NFS file locking. This can allow two VM processes to write the same files. Use it only if you have fencing in place and the source VM cannot keep writing to the same storage.

Expected VM Evacuation Outcomes

The table below shows the expected VM evacuation status as determined by the VM type (ephemeral or volume-backed), whether /opt/data/instances is shared (with or without nolock) for ephemeral VMs, and the host failure type (power loss or network isolation).

VM Type	/opt/data/instances Mount Status	Host Failure Type	VM Evacuation Status
Ephemeral	Not shared/mounted	Power loss	Success, with data loss
Ephemeral	Not shared/mounted	Network isolation	Success, with data loss
Ephemeral	Shared and mounted with nolock	Power loss	Success, no data loss
Ephemeral	Shared and mounted with nolock	Network isolation	Success, no data loss. VMs are paused on the source host
Ephemeral	Shared and mounted without nolock	Power loss	Success, no data loss
Ephemeral	Shared and mounted without nolock	Network isolation	Failure with Failed to write lock VM still running on isolated host
Volume-backed	Doesn't matter	Power loss	Success, no data loss
Volume-backed	Doesn't matter	Network isolation (NFS without nolock)	Failure with Failed to write lock VM still running on isolated host and continues to hold /opt/pf9/data/state/mnt/<id>/volume-<volume-uuid>
Volume-backed	Doesn't matter	Network isolation (NFS with nolock)	Success, no data loss. VMs are paused on the source host