OP:
you say your NAS became unresponsive, was it during a deletion of a bunch of data?
the error is (likely the ZIL being replayed) is trying to add a segment of free space twice to the space map which should never happen but can a large file deletion or destroy is in progress before an ungraceful reboot. this is one of the more common issues I’ve seen (and encountered).
first, try to see if you can import the read only, as I said above when this exact error usually happens it’s because the ZIL is trying to replay something that already happened during import which fails… readonly ignores the ZIL and I’m fairly certain it also doesn’t load spacemaps.
first, boot up your system with enough of the disks connected that it doesn’t automatically try to import the pool
when your system is up, reconnect the disks and try:
zpool import Data -o readonly=on
to import the pool readonly
you may want to try zpool import Data -F -o readonly=on
if the first try is unsuccessful…
however, if you can import the pool readonly you have some options:
- copy the data out and recreate the pool from scratch.
- try enabling
zil_replay_disable
before importing to throw out the ZIL if the ZIL is your problem (you will lose some recent transactions, and you will likely leak some space) - more drastic then the last… enable the
zfs_recover
tunable which will allow duplicate entries into the spacemap… this might be necessary if you have issues beyond the ZIL.
I’ve had success on a system that was hard shutdown due to “freezing” while deleting a rather large dataset, importing readonly worked, and separately importing with zfs_recover worked, and it was enough to let the zfs metaslab coalescing algorithms work and fix the issue naturally, the pool has been healthy since. here is the post that led me to try this, years ago
but it is important to understand what put your pool in this state, and what risk you are willing to take, data that you were already trying to delete is obviously less valuable so it may be acceptable to try these drastic measures… good luck.