On Wed, Jan 19, 2011 at 08:41:15PM +1100, NeilBrown wrote:
> All you need to do is get md/raid5 to try reading the bad block. Once it does
> that it will get a read error and automagically try to correct it.
So, if I get this right, raid5 only reads n-1 drives. Unless I'm unlucky
enough to have the bad disk be the parity stripe, just reading the file with
a bad stripe by luck would cause the kernel to recompute parity on the read
error and re-write the bad block?
(I also read in the online docs that raid4 actually reads all the blocks,
including parity, which is a bit slower, but would actually guarantee that
all blocks are read, and parity is still consistent at ready time?)
But back to your point: check, which I had started, will indeed do what I
was hoping it would, thanks.
> If you were really keen, you could
> cd /sys/block/mdXX/md
> echo 3907029168 > sync_min
> echo 3907029170 > sync_max
> echo check > sync_action
I stopped the full check, and tried:
gargamel:/sys/block/md7/md# cat sync_min
244188936
gargamel:/sys/block/md7/md# cat sync_max
max
gargamel:/sys/block/md7/md# echo 3907029168 > sync_min
bash: echo: write error: Invalid argument
Any idea what went wrong here?
gargamel:/sys/block/md7/md# mdadm --detail /dev/md7
/dev/md7:
Version : 1.02
Creation Time : Thu Mar 25 20:15:00 2010
Raid Level : raid5
Array Size : 7814045696 (7452.05 GiB 8001.58 GB)
Used Dev Size : 1953511424 (1863.01 GiB 2000.40 GB)
Raid Devices : 5
Total Devices : 5
Persistence : Superblock is persistent
Update Time : Wed Jan 19 09:27:57 2011
State : clean
Active Devices : 5
Working Devices : 5
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 512K
Name : gargamel.svh.merlins.org:7 (local to host gargamel.svh.merlins.org)
UUID : 5884576b:0e402a5d:8629093c:ec020760
Events : 28714
Number Major Minor RaidDevice State
0 8 129 0 active sync /dev/sdi1
1 8 145 1 active sync /dev/sdj1
2 8 161 2 active sync /dev/sdk1
3 8 177 3 active sync /dev/sdl1
5 8 113 4 active sync /dev/sdh1
As for docs, a bit of googling before posting didn't help. I since then
found the new README.checkarray in my /usr/share/doc (debian), so that helps
although it doesn't talk about check vs repair.
Also, I didn't find anything about sync_action, check, and repair in the
mdadm man page (a pointer to
https://raid.wiki.kernel.org/index.php/RAID_Administration
would me useful).
Actually the above page still says that you can't check just a range of blocks.
Is there more up to date documentation that I should be reading somewhere?
Thanks for your answer,
Marc
--
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems & security ....
.... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/
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