On Tue, Jul 24, 2018 at 2:03 PM Matthew B <matthew.has.questions(a)gmail.com&gt; wrote: This makes the vm depend on 3 storage domain - very fragile configuration. The two large disks are mirrored using ZFS - but when one of the storage I don't think we support this concept. When you start the vm, the disk must exists. If the disks are not needed when the vm starts, maybe you want to plug them to the vm later by your application, only if the disks are available? Even if you solved plugging the disks only when the storage is available, you need to handle errors while the disk is plugged to the vm. If qemu fail to read or write to the disk, it must choose: - pause the vm, so the I/O can be retried later when the vm is resumed - stop the vm, maybe the operation will succeed on another host - propagate the error the guest. This will like to make the file system in the guest read-only, which usually requires a restart of the vm to recover. The last option may work if the guest is using multipath, and multipath is configured to queue I/O forever on failures. Vdsm supports different error policy per drive, but I don't see any UI for setting this. You can see the error_policy in the vm xml, available in vdsm log when starting a vm, or using virsh virsh -r list find your vm id or name, and then: virsh -r dumpxml my-vm-name-or-id Arik, do we have a way to control error policy per disk? Another option is to mount the "optional" disks from within the vm, so your application inside the vm have full control when there is trouble to mount or access the optional disks. Nir