can't write block 64 on raidframe partition

I'm sure I've done something wrong with the setup of this machine, but
I'm at a loss to figure out what - so I'm hoping that publically
embarrassing myself will do the trick.  :)

I have a 4.0_BETA2 amd64 system with root on raid1 (raidframe) -
everything seems to work OK _except_ when I fsck the root partition:

** /dev/rraid0a
** File system is already clean
** Last Mounted on /
** Root file system
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
CG 0: PASS5: BAD MAGIC NUMBER
SUMMARY INFORMATION BAD
SALVAGE? [yn]      
SALVAGE? [yn] y

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


CANNOT WRITE: BLK 64
CONTINUE? [yn] y

THE FOLLOWING SECTORS COULD NOT BE WRITTEN: 64,
2523 files, 20001 used, 2560438 free (270 frags, 320021 blocks, 0.0%
fragmentation)


... it's always block 64.   I've set up dozens of root-on-raid1 systems,
and this is the first time I've run into this.  Could I have gotten some
offset wrong somewhere?

In case it triggers something for someone, here's the output of raidctl
-s, and the disklabels:

Components:
           /dev/wd0a: optimal
           /dev/wd3a: optimal
No spares.
Component label for /dev/wd0a:
   Row: 0, Column: 0, Num Rows: 1, Num Columns: 2
   Version: 2, Serial Number: 20070222, Mod Counter: 421
   Clean: No, Status: 0
   sectPerSU: 128, SUsPerPU: 1, SUsPerRU: 1
   Queue size: 100, blocksize: 512, numBlocks: 1465148928
   RAID Level: 1
   Autoconfig: Yes
   Root partition: Yes
   Last configured as: raid0
Component label for /dev/wd3a:
   Row: 0, Column: 1, Num Rows: 1, Num Columns: 2
   Version: 2, Serial Number: 20070222, Mod Counter: 421
   Clean: No, Status: 0
   sectPerSU: 128, SUsPerPU: 1, SUsPerRU: 1
   Queue size: 100, blocksize: 512, numBlocks: 1465148928
   RAID Level: 1
   Autoconfig: Yes
   Root partition: Yes
   Last configured as: raid0
Parity status: clean
Reconstruction is 100% complete.
Parity Re-write is 100% complete.
Copyback is 100% complete.

www1:riz  ~> sudo disklabel wd0
# /dev/rwd0d:
type: unknown
disk: Disk1   
label:
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 16
sectors/cylinder: 1008
cylinders: 1453521
total sectors: 1465149168
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # microseconds
track-to-track seek: 0  # microseconds
drivedata: 0

16 partitions:
#        size    offset     fstype [fsize bsize cpg/sgs]
 a: 1465149105        63       RAID                     # (Cyl.      0*-
1453520)
 c: 1465149105        63     unused      0     0        # (Cyl.      0*-
1453520)
 d: 1465149168         0     unused      0     0        # (Cyl.      0 -
1453520)
www1:riz  ~> sudo disklabel wd3
# /dev/rwd3d:
type: unknown
disk: Disk1   
label:
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 16
sectors/cylinder: 1008
cylinders: 1453521
total sectors: 1465149168
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # microseconds
track-to-track seek: 0  # microseconds
drivedata: 0

16 partitions:
#        size    offset     fstype [fsize bsize cpg/sgs]
 a: 1465149105        63       RAID                     # (Cyl.      0*-
1453520)
 c: 1465149105        63     unused      0     0        # (Cyl.      0*-
1453520)
 d: 1465149168         0     unused      0     0        # (Cyl.      0 -
1453520)
www1:riz  ~> sudo disklabel raid0
# /dev/rraid0d:
type: unknown
disk: raid
label:
flags:
bytes/sector: 512
sectors/track: 128
tracks/cylinder: 8
sectors/cylinder: 1024
cylinders: 1430809
total sectors: 1465148928
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # microseconds
track-to-track seek: 0  # microseconds
drivedata: 0

16 partitions:
#        size    offset     fstype [fsize bsize cpg/sgs]
 a:  10485760         0     4.2BSD      0     0     0  # (Cyl.      0 - 
10239)
 b:   2097152  10485760       swap                     # (Cyl.  10240 - 
12287)
 c: 1465148865        63     unused      0     0        # (Cyl.      0*-
1430809*)
 d: 1465148928         0     unused      0     0        # (Cyl.      0 -
1430809*)
 e:  20971520  12582912     4.2BSD      0     0     0  # (Cyl.  12288 - 
32767)
 f:  83886080  33554432     4.2BSD      0     0     0  # (Cyl.  32768 -
114687)
 g:  83886080 117440512     4.2BSD      0     0     0  # (Cyl. 114688 -
196607)
 h: 1263822336 201326592     4.2BSD      0     0     0  # (Cyl. 196608 -
1430809*)



...any ideas?

Thanks!
+j

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