Bare-metal, single node iSCSI SAN software with web-based UI that doesn't use ZFS, costs nothing and is actively developed

[nabsltd]

My ZFS based zvols, even on a pool that is 80% full, exported as a iscsi LUN fully support live migration of VM's without any downtime.

I never said you couldn't.

What I did say, though, that if you couldn't live migrate, you probably wouldn't be able to patch the iSCSI host system without the VMs noticing,

And, as for an 80% full pool and live migration...of course how full it is doesn't stop the migration, as long as there is enough space on the target pool to hold the VM. This is because migration works by taking a snapshot of the VM, redirecting writes to the new location, then copying all the data to from old to new, then moving the pointer to the base disk from old to new, then removing the snapshot (which pushes the new writes into the VM disk). The disk is never unavailable as far as the VM OS is concerned.

An 80% full pool, however, will slow down the migration a lot compared to a pool that is 25% or 50% full.

 

[BackupProphet]

When you live migrate with kvm, there is no need to copy the VM content that is stored on disk. You only copy memory pages, ie what you have in RAM. Also, I would not worry about filling up an enterprise ssd over 80%, the performance difference is negligible.

 

[BackupProphet]

When "patching" the iSCSI host system, you have some options. Most likely you have no need to update the system. You probably run your SAN on its own VLAN and the only services exposed is TGT(or whatever you use) and SSH. Check for CVE's for your iscsi host system. Most likely there have not been anything serious last 5 years.

You can use kpatch, to patch the kernel. A change to your iscsi host system will require restart of the iscsi host system, but it's probably fast enough and will not cause any issues with your VM.