Errors on a file on a zpool: How to remove?

[Rich]

Well, that's frustrating.

I moved all the data off of that FS on the pool, onto a newly-created
FS on the pool. It took a few days.

I just attempted to zfs destroy the old filesystem.

The command hung for 30 minutes, at which point I decided that this
was likely not doing anything useful, especially since operations to
all but the latest-created filesystem on the pool now hung, as well as
zfs list.

I got this fun thing out of /var/log/messages, too:
Jan 31 23:12:05 manticore root: ZFS: checksum mismatch, zpool=rigatoni
path=/dev/da5 offset=446136819712 size=8192
Jan 31 23:12:05 manticore root: ZFS: checksum mismatch, zpool=rigatoni
path=/dev/da2 offset=320393101312 size=8192
Jan 31 23:12:05 manticore root: ZFS: checksum mismatch, zpool=rigatoni
path=/dev/da4 offset=1231402180608 size=8192
Jan 31 23:12:05 manticore root: ZFS: checksum mismatch, zpool=rigatoni
path=/dev/da5 offset=446136819712 size=8192
Jan 31 23:12:05 manticore root: ZFS: checksum mismatch, zpool=rigatoni
path=/dev/da2 offset=320393101312 size=8192
Jan 31 23:12:05 manticore root: ZFS: checksum mismatch, zpool=rigatoni
path=/dev/da4 offset=1231402180608 size=8192
Jan 31 23:12:05 manticore root: ZFS: zpool I/O failure, zpool=rigatoni error=86
Jan 31 23:12:05 manticore root: ZFS: vdev I/O failure, zpool=rigatoni
path= offset= size= error=

The last one, of course, being fascinating.

Okay, how annoying. I try sysctl debug.kdb.panic=1, and it hangs. Uh-oh.

I reboot physically, and the system hangs on "Mounting local
filesystems..." for a long time.

I power the machine off, unplug all 5 devices in that pool, and boot
the machine again. It boots rapidly and fine.

I export the pool (now reporting that all 5 devices were missing,
unsurprisingly), power the machine off, plug the 5 devices back in,
and power on.

Machine boots. zpool import rigatoni succeeds. zfs list now hangs. df
output shows no filesystems from that pool, and /var/log/messages got
another copy of what I just pasted above.

Thoughts?

- Rich