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Old 05-16-2008, 09:48 AM   #1
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Question Keep RAID-5 Set on Fresh install

Hi All,

I have a simple question but have not yet found the answer.
My system has 6 disks, 2 in Raid-1 for the OS and 4 in Raid-5 for my data.
What I want to do is reinstall the OS (Ubuntu 7.10) ... but without loosing my Raid-5 Data set. How do I do this?

Will setup detect my drives and not wipe the data out?
Should I disconnect them and move back mdadm.conf ?? When I do this the lines won't match because when I reinstall with the disks disconnected the first set will become md2 (which is now assigned to the raid-5 set).

Please help me out, I am afraid to begin installing if I am not sure my data will be accessible. Thanks!

Some more info on my system:

root@Lawk:/etc# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md2 : active raid5 sdc1[0] sdf1[3] sde1[2] sdd1[1]
937705728 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]

md4 : active raid1 sda2[0] sdb2[1]
4923840 blocks [2/2] [UU]

md3 : active raid1 sda1[0] sdb1[1]
151364288 blocks [2/2] [UU]

unused devices: <none>

root@Lawk:/etc# cat mdadm/mdadm.conf
# mdadm.conf
# Please refer to mdadm.conf(5) for information about this file.

# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
DEVICE partitions

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts

# definitions of existing MD arrays
ARRAY /dev/md3 level=raid1 num-devices=2 UUID=0c7cf341:ca185eb2:3070bc8c:11a02322
ARRAY /dev/md4 level=raid1 num-devices=2 UUID=bda11432:d47dc94e:cbe7a488:aab5fc12
ARRAY /dev/md2 level=raid5 num-devices=4 UUID=c30c2978:8f09bd7e:158efcf4:9b81728d

# This file was auto-generated on Sun, 23 Sep 2007 14:04:29 +0000
# by mkconf $Id: mkconf 261 2006-11-09 13:32:35Z madduck $

root@Lawk:/etc# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/md3 143G 101G 35G 75% /
varrun 2.0G 2.9M 2.0G 1% /var/run
varlock 2.0G 0 2.0G 0% /var/lock
udev 2.0G 216K 2.0G 1% /dev
devshm 2.0G 0 2.0G 0% /dev/shm
lrm 2.0G 38M 1.9G 2% /lib/modules/2.6.22-14-generic/volatile
/dev/md2 881G 419G 418G 51% /Storage
Old 05-19-2008, 02:30 PM   #2
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These are some no doubt simple minded suggestions:

As a word of caution, I like to jump into cold water all at once instead of putting in one toe at a time. Having said that, I haven't tried ubuntu 7.1 setup on a raided system, however, there should be no harm in trying to see how smart the installer is, given a few precautions. BUT, backup your data and system before doing anything else.

The ubuntu installer will ask where to put things; if it doesn't look right (ie you don't know for sure that the disks it wants to install to are the ones you want to install to) - don't do it. Setup the system disks first, then set up raid 1 on the system disks (there's an excellent how-to on the ubuntu site): google "howto raid ubuntu" it's #1

If you don't let it touch the raid 5 disks, I doubt you'll have a problem rebuilding the raid 5 array after your new setup is complete.

good luck, let us know how it goes


mdadm, raid, software, ubuntu

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