I had created a pool in FreeNAS Corral (Virtualized under esxi 6.5). I created new VMs with 9.10 and napp-it and passed through the HBA to the new VMS. I was able to import them. I'm a complete neophyte when it comes to ZFS and dont understand what you mean by update the pools within Corral.
I'm very a much new to ZFS and FreeNAS myself but what I've been reading is that if you hit the upgrade button for your volumes (as pictured below) after installing Corral you can't simply import those volumes back into FreeNAS 9.10 because that upgrade button introduced some features only available in FreeBSD 11 where 9.10 is based on FreeBSD 10.
I unfortunately hit upgrade by mistake on one of my two volumes and thus I can't import that volume back into 9.10 without using the "NIGHTLY" train which itself is not stable. Of course this volume I upgraded by mistake is the main one I need
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EDIT: Check that, they have revised their post on this. I might be fine after all.
FreeNAS Corral - Migrating from FreeNAS Corral to FreeNAS 9.10
I never used 9.10!
I upgraded my pool!
Well, that complicates things a little bit. FreeNAS Corral uses FreeBSD 11, which adds support for some ZFS features not available in FreeBSD 10, which 9.10.2 uses. FreeNAS 9.10.3 will be based on FreeBSD 11 and will allow you to import your pool. You can either wait for the Release, scheduled for May, or try out the nightlies.
Good news! FreeBSD 11 only adds two feature flags: sha512 and skein for hashing and dedup. Most users will not have actually used these in any dataset, so they should still be marked as "enabled", so pools that were either upgraded or created in Corral will mostly just import in 9.10.2. If you actually used either of these feature flags, you most likely knew what you were getting yourself into.