RAID

keith ralph · 04-25-2006, 06:49 AM

Hi - I have a configuration issue with mdadm RAID1
I have 4 LUNS - sda/sdb on 1 path and sdc/sdd on 2nd path
I have /dev/sda mirrored to /dev/sdc and sdb mirrored to sdd.On a reboot mdadm seems to establish the mirrors starting at sdd then sdc then sdb then sda. I want to force sda to be the primary disc and resync with sdc.
I have expilictly updated /etc/mdadm.conf so that theree is no DEVICE=partitions ie

ARRAY /dev/md1 level=raid1 num-devices=2 UUID=8ca1bd25:449a5a09:9aab01a9:ca68cbfa
devices=/dev/sda2
ARRAY /dev/md2 level=raid1 num-devices=2 UUID=1af61e1f:5e49f5ab:39b62b46:626daaea
devices=/dev/sdb1
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=25889e7a:e6f01deb:b9487c5a:06fd043d
devices=/dev/sda1

but it still forms the array from /dev/sdc

Any help much appreciated

WhatsHisName · 04-26-2006, 12:22 AM

Don’t think you can change the member device order without recreating the raids.

Or said another way, you would need to stop each raid and recreate it with member devices in the desired order. Be sure to backup everything first.

Also, mdadm.conf isn’t used to create or manage the raids. It’s more there to tell the OS what to expect. mdadm-based raids are self sufficient and are not OS dependent.

keith ralph · 05-03-2006, 09:42 AM

I'm not sure how I stop the raid and recreate it in the right order - looking at /var/log/messages it seems to interogate sdd first then sdc then b then a.

Thanks whatsyourname :-)

WhatsHisName · 05-03-2006, 10:53 AM

Everything listed below can be found in the (incredibly long) mdadm man page.

Don’t blindly use the following commands. Be sure you understand what they do before you proceed.

With md1 and md2 unmounted:

Code:

# # Verify that md1 and md2 are synced and clean
#
# mdadm -D /dev/md1   # OR “cat /proc/mdstat”
# e2fsck -f /dev/md1  # OR fsck whatever type of filesystem you are using
#
# # Stop and recreate raid1
#
# mdadm -S /dev/md1
# mdadm -C /dev/md1 -l1 -n2 /dev/sda1 missing
# e2fsck -f /dev/md1  # OR fsck whatever type of filesystem you are using
#
# #  Then mount md1 and verify that the contents look OK.
# #  If md1 looks fine, then:
#
# mdadm /dev/md1 -a /dev/sdc1
# cat /proc/mdstat
#
# #  If md1 does not look correct, then unmount it and:
#
# mdadm -S /dev/md1
# mdadm -A --run /dev/md1 /dev/sdc1
# e2fsck -f /dev/md1  # OR fsck whatever type of filesystem you are using
# mdadm /dev/md1 -a /dev/sda1
# cat /proc/mdstat

And likewise for md2 after md1 is rebuilt.

As a warning, I don’t recall doing this on a real filesystem, but since the partitions are already set up for software raid1, the recreation should work fine. As always, be sure to back up everything before you start.

keith ralph · 05-05-2006, 09:10 AM

Thanks for your help - I'll give it a try