[zfs-discuss] How recoverable is an 'unrecoverable error'?

[Uwe Dippel]

My question is related to this:

# zpool status
 pool: rpool
state: ONLINE
status: One or more devices has experienced an unrecoverable error.  An
   attempt was made to correct the error.  Applications are unaffected.
action: Determine if the device needs to be replaced, and clear the errors
   using 'zpool clear' or replace the device with 'zpool replace'.
  see: http://www.sun.com/msg/ZFS-8000-9P
scrub: scrub completed after 0h46m with 0 errors on Tue Apr 14 00:19:34 
2009
config:
   NAME        STATE     READ WRITE CKSUM
   rpool       ONLINE       0     0     0
     c1d0s0    ONLINE       0     0     1
errors: No known data errors

Since it is a rather new drive and has no trouble with Ubuntu, I dared 
to clean it:
# zpool clear rpool
and checked it for errors:
# zpool scrub rpool
# zpool status -v
 pool: rpool
state: ONLINE
scrub: scrub completed after 0h47m with 0 errors on Tue Apr 14 23:53:48 
2009
config:
   NAME        STATE     READ WRITE CKSUM
   rpool       ONLINE       0     0     0
     c1d0s0    ONLINE       0     0     0
errors: No known data errors

Now I wonder where that error came from. It was just a single checksum 
error. It couldn't go away with an earlier scrub, and seemingly left no 
traces of badness on the drive. Something serious? At least it looks a 
tad contradictory: "Applications are unaffected.", it is unrecoverable, 
and once cleared, there is no error left.

Curious,

Uwe