Frustration: replace not doing what I expected.

[Baldur Gislason]

A drive failed in a pool and I had to replace it.
I did zpool replace ad18 ad18, the pool resilvered for 5 hours
and finished but did not return from degraded mode.
I tried removing the cache file and reimporting the pool, no change, it
hasn't gotten rid of the old drive which does not exist anymore.

What to do?

Baldur

  pool: zirconium
 state: DEGRADED
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.
   see: http://www.sun.com/msg/ZFS-8000-8A
 scrub: none requested
config:

        NAME                       STATE     READ WRITE CKSUM
        zirconium                  DEGRADED     0     0     0
          raidz1                   DEGRADED     0     0     0
            ad4                    ONLINE       0     0     0
            ad6                    ONLINE       0     0     0
            replacing              DEGRADED     0     0     0
              2614810928866691230  UNAVAIL      0   962     0  was /dev/ad18/old
              ad18                 ONLINE       0     0     0
            ad20                   ONLINE       0     0     0