Experimente zpool import -f -F -n filetank
.
Isso não importará o pool, mas dirá se é recuperável.
Se isso der a luz verde, prossiga:
zpool import -f -F filetank
Detalhes sobre essas opções, na página man:
-f
Forces import, even if the pool appears to be poten-
tially active.
-F
Recovery mode for a non-importable pool. Attempt to
return the pool to an importable state by discarding
the last few transactions. Not all damaged pools can
be recovered by using this option. If successful,
the data from the discarded transactions is irre-
trievably lost. This option is ignored if the pool
is importable or already imported.
...
-n
Used with the -F recovery option. Determines whether
a non-importable pool can be made importable again,
but does not actually perform the pool recovery. For
more details about pool recovery mode, see the -F
option, above.