Filesystem corruption when drives are mirrored, but not otherwise

[Alastair Rankine]

The story is this: two identical WD 250GB SATA drives, attached to a  
Promise FastTrak S150 TX2plus.

The drives work fine independently (ie non-mirrored). But when I  
mirror them using GEOM, I get filesystem corruption (see below for  
example fsck output).

I have tried each drive independently as a provider for the GEOM  
mirror. First ar4 then ar6, not a single instance of filesystem  
corruption. But with both drives, I start to get filesystem  
corruption after only a few hours of light use.

Some relevant points:

     * This does not seem to be GEOM related. I got the same problem  
using the two drives in a mirrored configuration using the onboard  
Promise BIOS. Although I could not (easily) test the drives  
independently using the Promise BIOS, I am reasonably sure the  
mirrored configuration results were the same for GEOM as for the  
Promise BIOS.
     * The drives are identical and of similar age.
     * Using smartmontools I have found no SMART errors on either of  
the two drives.
     * I am running FreeBSD-STABLE. I originally found this problem  
when I first installed FreeBSD on this machine (6.0-RELEASE at the  
time). I upgraded to -stable to pick up some ataraid fixes (at the  
time I was running off the Promise BIOS), which (obviously) did not  
fix the problem.
     * The machine boots off a 18GB SCSI disk attached to an Adaptec  
controller. This drive has performed flawlessly and does not exhibit  
any of the filesystem corruption of the mirrored drives.
     * The drives are mostly accessed over the network via NFS or SMB.

This has me totally confused - I don't even know if it's hardware or  
software related. The only thing I can think of is to swap the  
Promise controller card, but that's prettymuch a last resort. Any  
help appreciated.

Example fsck output follows.


/ $ fsck /home
** /dev/mirror/gm0s1a
** Last Mounted on /home
** Phase 1 - Check Blocks and Sizes
UNKNOWN FILE TYPE I=17287183
UNEXPECTED SOFT UPDATE INCONSISTENCY

CLEAR? [yn] y

PARTIALLY ALLOCATED INODE I=20066351
UNEXPECTED SOFT UPDATE INCONSISTENCY

CLEAR? [yn] y

** Phase 2 - Check Pathnames
UNALLOCATED  I=17287183  OWNER=root MODE=0
SIZE=0 MTIME=Jan  1 10:00 1970
NAME=/music/iTunes/Coldcut/Let Us Play/._1-07 Noah's Toilet.m4a

UNEXPECTED SOFT UPDATE INCONSISTENCY

REMOVE? [yn] y

** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
FREE BLK COUNT(S) WRONG IN SUPERBLK
SALVAGE? [yn] y

SUMMARY INFORMATION BAD
SALVAGE? [yn] y

BLK(S) MISSING IN BIT MAPS
SALVAGE? [yn] y

30075 files, 24370829 used, 93886060 free (3100 frags, 11735370  
blocks, 0.0% fragmentation)

***** FILE SYSTEM WAS MODIFIED *****