Hi Everyone,
First off, a little background on my setup.
Ubuntu 7.10 i386 Server (2.6.22-14-server)
upgraded to
Ubuntu 8.04 i386 Server (2.6.24-19-server)
I have 8 SATA drives connected and the drives are organized into three
md RAID arrays as follows:
/dev/md1: ext3 partition mounted as /boot, composed of 8 members (RAID
1) (sda1/b1/c1/d1/e1/f1/g1/h1)
/dev/md2: ext3 partition mounted as /root, composed of 8 members (RAID
1) (sda2/b2/c2/d2/e2/f2/g2/h2)
/dev/md3: ext3 partition mounted as /mnt/raid-md3, composed of 8
members (RAID 6) (sda3/b3/c3/d3/e3/f3/g3/h3), this is the main data
partition holding 2.7TiBs worth of data
All the raid member partitions are set to type "fd" (Linux RAID
Autodetect).
Important Note: 6 of the drives are connected to two Sil3114 SATA
controller cards whilst 2 of the drives are connected to the on-board
SATA controller (I don't know which model it is).
After upgrading my Ubuntu installation to 8.04, upon system restart
there was an error message saying that my RAID arrays were degraded
and thus the system was unable to boot from it.
At the time, not knowing the cause of the sudden RAID failure, I
attempted to force mdadm to start the arrays anyways (the RAID 1
arrays with 8 members each were no causes for concern, of course, but
I wanted to back up my data on the degraded md3 array as soon as
possible).
Then it hit me, why would it recognize only 6 drives? Apparently the
kernel has some compatibility problems with certain SATA controllers
and my on-board controller chip was one of them.
Sure enough, after moving all 8 drives to the Silicon Image
controllers, the drives were all recognized without any problems.
If the missing drives were recognized again before the array was ever
brought up again, everything would've been fine. But unfortunately I
forced mdadm (--run switch) to bring it online with 2 missing members.
This is when the problem began. I know that as soon as I re-add the
two missing drives back into the md3 (RAID 6) array, the system will
attempt to rebuild the array, using the information from the remaining
6 drives.
Given the size of the array and the type of the disk drives being used
(off-the-shelf SATA drives with bit error rate of 1 out of 10^14
bits), I think it is highly likely that the system will encounter one
or more bit errors during the rebuild.
Anyway, I panicked and brought the md3 array down first to prevent
possible further damage.
So, at this stage what I'm wondering is:
1. If mdadm encounters a bit error during a RAID 6 rebuild, will it
just give up on that particular file and move on to recover other data
on the array? Or will it trash the entire array?
2. Is it possible to cheat mdadm by somehow replacing the new "raid
metadata" on the 6 drives with the old data on the 2 drives? Will it
make mdadm think the array is clean, consistent and nothing ever
happened?
Please do note that I did not write ANY new data onto the RAID 6 array
from the time it was degraded until the time I brought it down with (--
stop).
Sorry for the long post and thank you for your time in advance. I
really hope to get this RAID array back up without data corruption
because I don't have a working backup of the array (I know, very
stupid of me).
Dave
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
