zfs discuss - Nov 2011 - "zfs hold" and "zfs send" on a readonly pool

Hello, all.

   I''m in the process of repairing a corrupted unmirrored rpool,
and my current idea was to evacuate all reachable data by "zfs
send" to the redundant data pool, then recreate and repopulate
the rpool with copies=2.

   As I previously wrote, my machine crashes when trying to
import the rpool in any sort of read-write mode, however I
got it to import with readonly=on.

   I struck an unexpected problem: modern "zfs send" uses the
"zfs hold" feature to lock the snapshots from destruction.
However, on a readonly pool the holds don''t succeed and the
send never occurs:

root at openindiana:~# zfs send -R rpool/ROOT/oi_148a at 20111028-01 | \
   zfs recv -vnFd pool/rpool-backup
cannot hold ''rpool/ROOT/oi_148a at 20110317-03'': pool is
read-only
cannot hold ''rpool/ROOT/oi_148a at 20110319-01'': pool is
read-only
cannot hold ''rpool/ROOT/oi_148a at 20110322-01'': pool is
read-only
cannot hold ''rpool/ROOT/oi_148a at 20110401'': pool is
read-only
cannot hold ''rpool/ROOT/oi_148a at 20110430'': pool is
read-only
cannot hold ''rpool/ROOT/oi_148a at 20111028-01'': pool is
read-only

   IMHO this is a bug (some checks are due in zfs code - this
is an oi_148a liveusb); however - are any workarounds possible
with this code as is? Perhaps, some kernel tunables to set
with MDB?

   Of course, I can cpio this data both ways with little loss
in this case, but the problem for broken pool evacuation was
unexpected. I should''ve at least reported it ;)

Thanks for any ideas,
and good luck fixing it for the future ,)
//Jim Klimov