Glad to help. In a way I sort of like software RAID better than hardware
RAID, because of workarounds like this. I've had a 3ware hardware raid
card fail, and there was nothing I could do until I snagged another
3ware card from ebay. I also had an old promise raid card drop 2
drives at once, but there was no option to force the array back together
without a rebuild. I have so far been lucky enough to recover from
multi-drive failures every time when using software RAID. As far as
performance, I benchmarked a server we have that has a 12 disk software
RAID5, and it got the highest IO of any server I had tested, and that
was with crappy ATA-133 PATA drives. I also experience lots of problems
with those darn Dell PERC raid controllers - they seem to like to flake
out for no reason.
Joe Fleming wrote:
You're my savior man! I found a post on some forum talking about using
mdadm --examine to check the superblock on the drives. /dev/sdc1 was a
complete no show, but /dev/sdd1 (which was also failed) looked ok,
though outdated. I deactivated the array with mdadm --stop /dev/md0
and forced an assemble with the command you gave me.
mdadm --assemble --force /dev/md0 /dev/sda1 /dev/sdb1 /dev/sdd1
And I'm back online! Time to copy files off ASAP. I still hear the
chirping noise, from one of the drives, but at least it's back up.
Thanks again!
-Joe
Charles Jones wrote:
Joe Fleming wrote:
Hey all, I have a Debian box that was acting as a 4 drive RAID-5
mdadm softraid server. I heard one of the drives making strange
noises but mdstat reported no problems with any of the drives. I
decided to copy the data off the array so I had a backup before I
tried to figure out which drive it was. Unfortunately, in the middle
of copying said data, 2 of the drives dropped out at the same time.
Since RAID-5 is only tolerant to one failure at a time, basically
the whole array is hosed now. I've had drives drop out on me before,
but never 2 at once. Sigh.
I tried to Google a little about dealing with multi-drive failures
with mdadm, but I couldn't find much in my initial looking. I'm
going to keep digging, but I thought I'd post a question to the
group and see what happens. So, is there a way to tell mdadm to
"unmark" one of the 2 drives as failed and try to bring up the array
again WITHOUT rebuilding it? I really don't think both of the drives
failed on me simultaneously and I'd like to try to return 1 of the 2
to the array and test my theory. If I can get the array back up, I
can either keep trying to copy data off it or add a new replacement
and try to rebuild. I'm pretty novice with mdadm thought I don't see
an option that will let me do what I want. Can anyone offer me some
advice or point me in the right direction..... or am I just SOL?
As a side note, why can't hard drive manufacturers make drives that
last anymore? I've had like 5 drives fail on me in the last year...
WD, Seagate, Hitachi, they all suck equally! I can't find any that
last for any reasonable amount of time, and all the warranties leave
you with reman'd drives which fail even more rapidly, some even show
up DOA. Plus, I'm not sending my unencrypted data off to some random
place! Sorry for venting, just a little ticked off at all of this.
Thanks in advance for any help.
-Joe
I've had luck in the past recovering from a multi-drive failure,
where the other failed drive was not truly dead but rather was
dropped because of an IO error caused by a thermal calibration or
something similar. The trick is to re-add the drive to the array and
using the option to force it NOT to try to rebuild the array. This
used to be an require several options like --really-force and
--really-dangerous but now I think its just something like --assemble
--force /dev/md0. This forces the array to come back up to its
degraded (still down 1 disk) state. If possible replace the degraded
disk or copy your data off before the other flakey drive fails.
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