Hi,
> I'll wait for these details before I start hunting further.
OK, here we are.
Some forewords, the last disk to fail at boot was
/dev/sda, this data was collected after a "clean"
add of the /dev/sda3 to the RAID.
This means the superblock was zeroed and the device
added, so it should be clean.
mdadm --examine /dev/sda3
/dev/sda3:
Magic : a92b4efc
Version : 1.1
Feature Map : 0x1
Array UUID : b601d547:b62e9563:2c68459c:22db163f
Name : root
Creation Time : Tue Feb 10 15:43:09 2009
Raid Level : raid10
Raid Devices : 2
Avail Dev Size : 483941796 (230.76 GiB 247.78 GB)
Array Size : 483941632 (230.76 GiB 247.78 GB)
Used Dev Size : 483941632 (230.76 GiB 247.78 GB)
Data Offset : 264 sectors
Super Offset : 0 sectors
State : active
Device UUID : f3665458:d51d27f5:87724fb8:529f91f1
Internal Bitmap : 8 sectors from superblock
Update Time : Tue Feb 24 09:03:46 2009
Checksum : 68a2de81 - correct
Events : 6541
Layout : near=1, far=2
Chunk Size : 64K
Array Slot : 3 (failed, failed, 1, 0)
Array State : Uu 2 failed
mdadm --examine-bitmap /dev/sda3
Filename : /dev/sda3
Magic : 6d746962
Version : 4
UUID : b601d547:b62e9563:2c68459c:22db163f
Events : 6541
Events Cleared : 6540
State : OK
Chunksize : 256 KB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 241970816 (230.76 GiB 247.78 GB)
Bitmap : 945199 bits (chunks), 524289 dirty (55.5%)
Now, one thing I do not understand, but maybe it is
anyway OK, and it is this last line:
Bitmap : 945199 bits (chunks), 524289 dirty (55.5%)
Because the array status was fully recovered (in sync)
and /dev/sdb3 showed:
Bitmap : 945199 bits (chunks), 1 dirty (0.0%)
Confirmed somehow by /proc/mdstat
How it could be 55.5% dirty? Is this expected?
Further note.
I tested, on an identical PC, with a slightly different
RAID (metadata 1.0 vs. 1.1), the following:
mdadm --fail /dev/md2 /dev/sdb3
wait a little
mdadm --remove /dev/md2 /dev/sdb3
do something to make the bitmap a bit dirty
mdadm --re-add /dev/md2 /dev/sdb3
wait for resync to finish with "watch cat /proc/mdstat"
echo check > /sys/block/md/md2/sync_action
watch cat /proc/mdstat /sys/block/md/md2/mismatch_cnt
Now, immediatly the mismatch count went to something
like 1152 (or similar).
After around 25% of the check it was around 1440,
then I issued an "idle" and re-added the disk cleanly.
This repeats the experience I already had.
This is still a RAID-10 f2, with header 1.0, chunk 64KB
and bitmap chunksize of 16MB (or 16384KB).
Somehow it seems, at least on this setup, that
the bitmap does not track everything or the
resync does not consider all the bitmap chunk.
Thanks,
bye,
--
piergiorgio
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