I ran into this error when my NVMe SSD used for log & l2arc failed and could not boot.
Mounting from zfs:zroot/ROOT/default failed with error 6.
Trying to recover from a livecd was not helping. I could import the pool, but not remove the device.
Trying to offline the device would return a different error --
cannot offline 16642195929625272860: log device has unplayed intent logs
I ended up building a custom zfs.ko with the attached patch which I derived from this ZoL Github issue: https://github.com/zfsonlinux/zfs/issues/4270
This allowed me to make the pool usable again. After a scrub things are mostly OK now, though I have one mysterious error left; the other errors it reported are now gone.
root@colo:/usr/src # zpool status -v
status: One or more devices has experienced an error resulting in data
corruption. Applications may be affected.
action: Restore the file in question if possible. Otherwise restore the
entire pool from backup.
scan: scrub repaired 0 in 0 days 20:14:51 with 0 errors on Fri Jun 7 15:58:42 2019
NAME STATE READ WRITE CKSUM
zroot ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
da4p3.eli ONLINE 0 0 0
da5p3.eli ONLINE 0 0 0
mirror-1 ONLINE 0 0 0
da0p3.eli ONLINE 0 0 0
da2p3.eli ONLINE 0 0 0
mirror-2 ONLINE 0 0 0
da1p3.eli ONLINE 0 0 0
da3p3.eli ONLINE 0 0 0
errors: Permanent errors have been detected in the following files:
Created attachment 204889 [details]
patch to allow removing a log device with intent logs