TrueNAS and QNAP (with their QES OS) both offer HA ZFS platforms but with precious little documentation on how they’re accomplishing that. I get the impression from their hardware choices that both nodes mount both all disks simultaneously so it might just be a simple zfs import when the active node goes down but neither vendor seems to share a claim on failover speed so I may be way off target. Importing a 500 TB pool is not going to be quick enough to save your Samba sessions.
Anyone have experience with how these platforms implement HA on ZFS and if the failover is transparent to SMB clients?