ZFS - scrub lead to corruption?

[Paul Pathiakis]

Hi,

My ZFS-only machine running on 8.0-stable as of ???? is down hard.  It is a mirrored pair of Segate 1500 GB drives (yes, I know the firmware history of these drives and they are a late version.)  The sequence of events is as follows:

1) cvsup ports
2) portupgrade -a -r -p
3) everything completes successfully.
4) cvsup the latest 8.0 code.
5) make buildworld
6) while it was compiling, it requested m4 and said "not found"
7) which m4 -> not found
8) I find that /usr/bin/m4 is "there" with ls /usr/bin/m4.
9) cd /usr/ports/devel/m4 -> /usr
10) make; make deinstall; make package;  no issues.
11) cd /usr/src; make buildworld.  Same behavior.
12) ls -sal /usr/bin/m4 -> Panic
13) Reboot
14) zpool status web
everything is fine and online. :-)  No errors.
15) zpool scrub web
16) scrub continues to over 75% (I wasn't watching for the exact #) and then *panic* level 12
17) I reboot single user.
18) It mounts the web at /
19) At that point, I'm deciding what to do and .... Panic level 12  (I assume ZFS was scrubbing in the background and killed me.
20) Help!

How do I recover from this and what additional information does anyone need?  I know there's no fsck on ZFS but how do I rollback prior to the writes that caused this?  Also, I never enabled snapshots or anything else outside of mirroring.

Thank you for the help,

Paul