Rescue software RAID system

[William Muriithi]

> > So I booted from a rescue CD, used mdadmin to start RAID device,
mounted the
> > device and tried to chroot into the mount directory and don't work,
don't
> > seem to have chroot binary in my rescue environment.
>
> If this is the centos rescue environment, it definitely should include
> chroot. The approach you're taking seems fine to me. I've done this in
> the past.

This eventually worked. I have now been able to bring up one of the RAID
device up fully. This is md0 which is RAID1. I have struggled with md2
though which is a RAID5 device. Here is how it looks.

mdadm --query --detail /dev/md2

/dev/md2: Version : 1.2 Creation Time : Thu Dec 13 11:04:35 2012 Raid Level
: raid5 Used Dev Size : -1 Raid Devices : 3 Total Devices : 2 Persistence :
Superblock is persistent

Update Time : Thu Nov 21 09:20:07 2013 State : active, degraded, Not
Started Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare
Devices : 0

Layout : left-symmetric Chunk Size : 512K

Name : gfs1.jamar.com:2 (local to host gfs1.jamar.com) UUID :
0202547e:d9a3bd67:fdeaf168: a780aa38 Events : 6292

Number Major Minor RaidDevice State 0 0 0 0 removed 1 8 18 1 active sync
/dev/sdb2 3 8 34 2 active sync /dev/sdc2

mdadm --add /dev/md2 /dev/sda2 mdadm: add new device failed for /dev/sda2
as 4: Invalid argument

On dmesg, I see the error

MD2: ADD_NEW_DISK not supported

(The above actually worked for the RAID 1 device on the same system. It has
two partition, RAID 1 being system and RAID 5 being data partition).

mdadm --examine /dev/sd[abc]2 | egrep 'dev|Update|Role|State|Chunk Size'
/dev/sda2: State : active Update Time : Thu Nov 21 09:20:07 2013 Device
Role : spare Array State : AAA ('A' == active, '.' == missing) /dev/sdb2:
State : active Update Time : Thu Nov 21 09:20:07 2013 Device Role : Active
device 1 Array State : AAA ('A' == active, '.' == missing) /dev/sdc2: State
: active Update Time : Thu Nov 21 09:20:07 2013 Device Role : Active device
2 Array State : AAA ('A' == active, '.' == missing)

What does "used device size" mean when the number is negative?

Anybody see something I may have approached wrongly? Its a back up system
so not too worried for now. Plan to just destroy the device and create a
new if I can't bring it up by end week. Would be satisfying though to bring
it back though

William
>
> Also, in the unfortunate event that you have problems during the
> rebuild, be aware that unless the first failed disk is completely
> fubared, you may be able to use some of its data if required.
> Hopefully not, but keep it in mind.
>
> Thanks
> -Ben
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