I would expect this question to be answered in the FAQ, but the site
seems to be down. At least I can't get to it now. I'm sure this is
simple, but I want to be sure I get it right the first time and don't
mess up the data.
I have a system with 5 drives: a system/boot drive and a RAID5 composed
of 3 active drives and a spare (formated in ext3). The boot/system
drive died on me the other day and I've restored it, re-installing
Debian Sarge. The RAID drives were not effected by the failure.
Now that the system is up and running, I want to restore the RAID.
I've been searching and tried:
mdadm --examine --scan /dev/hde /dev/hdf /dev/hdg /dev/hdh
and got:
ARRAY /dev/md0 level=raid5 num-devices=3
UUID=d6fd4af2:5e5d0da2:9dec7c5f:ad60c25d
devices=/dev/hdf
I'm a little puzzled by this, since I created the drive specifying hde
first, and would expect mdadm to find that drive and not hdf. It also
finds only that one drive and does not seem to see hde or hdg as part
of the RAID.
When I tried
mdadm --examine /dev/hdf
I got:
/dev/hdf:
Magic : a92b4efc
Version : 00.90.00
UUID : d6fd4af2:5e5d0da2:9dec7c5f:ad60c25d
Creation Time : Fri Dec 9 12:41:00 2005
Raid Level : raid5
Raid Devices : 3
Total Devices : 4
Preferred Minor : 0
Update Time : Fri Dec 9 15:44:21 2005
State : clean
Active Devices : 3
Working Devices : 4
Failed Devices : 0
Spare Devices : 1
Checksum : ba586641 - correct
Events : 0.82
Layout : left-symmetric
Chunk Size : 64K
Number Major Minor RaidDevice State
this 3 34 64 3 spare /dev/hdh
0 0 33 0 0 active sync /dev/hde
1 1 33 64 1 active sync /dev/hdf
2 2 34 0 2 active sync /dev/hdg
3 3 34 64 3 spare /dev/hdh
That made me feel better, since it shows me that at least mdadm "knows",
somehow, the structure and all the disks in the RAID.
When I type the same for any other drive, I get (depending on the drive
letter):
mdadm: No super block found on /dev/hdg (Expected magic a92b4efc, got
00000000)
Is this correct? Is there only one superblock and not one per drive?
(I may have misunderstood that.)
I thought, from the man page, that I could type:
mdadm --assemble --scan and have it assemble the RAID again, but that
doesn't. I've tried a few combinations, but nothing seems to work. I
get errors and it seems I need to include info in the config file to
make it work.
I've seen a fair number of tutorials on setting up RAID drives, but
almost nothing on restoring one that exists. I guess this would be
treated the same as if I were moving it from one computer to another.
I've found some info on this in the archives of this list, but nothing
that actually addressed this issue (I'm still searching, though).
Before anyone asks about backups, I don't have an exact backup (don't
yet have the space and equipment), but I can restore the data. Doing
so will take time and I'd really like to know how to take care of this
so if it happens in the future with a drive I need restored quickly,
I'll be sure to know how to handle it.
I feel like I'm being lazy asking this outright, but should there be
just a single command using --scan and --assemble and a few options
that will rebuild this and mount it as md0?
Thanks for any help on this -- and if anyone knows of a mirror of the
FAQ, I'd like the link since I can't get the original site to load.
Hal
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