Expanding a RAID-5 in use from 3 disks to 6 disks

Hello,

I've being trying to set a 6 disk RAID-5 for a few days but it took only 3 disks (the other 3 gave Device busy error); in the meantime, an old server went out of order so I have to use the incomplete host and it is now online with user files.

The question is, is there a way to expand my RAID-5 from 3 disks to 6 disks without losing data?.

Below is the basic information I could collect.

Best Regard,

Adrian Costoya
Metrovision Producciones S.A.
Buenos Aires - Argentina

[root@NAS-1 /]# uname -a
Linux NAS-1 2.6.18-1.2798.fc6xen #1 SMP Mon Oct 16 15:11:19 EDT 2006 i686 i686 i386 GNU/Linux

[root@NAS-1 /]# mdadm -V
mdadm - v2.6.1 - 22nd February 2007

[root@NAS-1 /]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdc1[3](S) sdb1[4](S) sde1[0] sda1[5](S) sdd1[2] sdf1[1]

      625137152 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]

unused devices: <none>

[root@NAS-1 /]# mdadm --detail /dev/md0
/dev/md0:

        Version : 00.90.03

Creation Time : Tue May 15 12:37:48 2007
Raid Level : raid5
Array Size : 625137152 (596.18 GiB 640.14 GB)
Used Dev Size : 312568576 (298.09 GiB 320.07 GB)
Raid Devices : 3
Total Devices : 6
Preferred Minor : 0
Persistence : Superblock is persistent

Update Time : Thu Jul 5 19:17:52 2007
State : clean
Active Devices : 3
Working Devices : 6
Failed Devices : 0
Spare Devices : 3

Layout : left-symmetric
Chunk Size : 64K

UUID : e5842e95:a8f9aa19:fe6f0d66:a15f32ab
Events : 0.72

Number Major Minor RaidDevice State
0 8 65 0 active sync /dev/sde1
1 8 81 1 active sync /dev/sdf1
2 8 49 2 active sync /dev/sdd1

3 8 33 - spare /dev/sdc1
4 8 17 - spare /dev/sdb1
5 8 1 - spare /dev/sda1
[root@NAS-1 /]#

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Yes, it's possible. A quick google of 'linux expand raid 5' turned up a bunch of hits, FYI.

Since you already have the 3 disks added to the array as spares, all you should have to do is:

mdadm --grow /dev/md0 --raid-devices=6

Watch /proc/mdstat for the expansion status.

After it is complete, you need to expand your filesystem to utilize the new larger device.

Keep in mind that most people recommend raid 6 for larger raid 5 arrays since the likelyhood of multiple device failures goes up significantly the more drives you have in your array. Unfortunately I don't think it is possible to convert a raid 5 array to raid 6.

-Dave