Upgrading Disks in a Software Raid System

Posted on August 28th, 2011 in General,Linux System Administration by Brandon

I have a system at home with a pair of 640 GB drives, that are getting full. The drives are configured in a Linux Software RAID1 array. Replacing those drives with a pair of 2 TB drives is a pretty easy (although lengthy process).

First, we need to verify that our RAID system is running correctly. Take a look at /proc/mdstat to verify that both drives are online:

root@host:~# cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md1 : active raid1 sdb3[1] sda3[0]
      622339200 blocks [2/2] [UU]

md0 : active raid1 sdb1[1] sda1[0]
      192640 blocks [2/2] [UU]

After verifying that the system is running, I powered the machine off and removed the second hard drive and replaced it with the new drive. Upon starting it back up, Ubuntu noticed that the RAID system was running in degraded mode and I had to hit yes at the console to have it continue booting.

Once the machine was running, I logged in and created a similar partition structure on the new drive using the fdisk command. On my system, I have a small 200 partition for /boot as /dev/sdb1, a 1 GB swap partition, and then the rest of the drive is one big block for the root partition. The I copied the partition table that was on /dev/sda, but for the final partition, made it take up the entire rest of the drive. Make sure to set the first partition as bootable. The partitions on /dev/sdb now look like this:

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          24      192748+  fd  Linux raid autodetect
/dev/sdb2              25         146      979965   82  Linux swap / Solaris
/dev/sdb3             147      243201  1952339287+  fd  Linux raid autodetect

After the partitions match up, I can now add the partitions on /dev/sdb into the RAID array

root@host:~# mdadm --manage /dev/md0 --add /dev/sdb1
root@host:~# mdadm --manage /dev/md1 --add /dev/sdb3

And watch the status of the rebuild using

watch cat /proc/mdstat

After that was done, I installed grub onto the new /dev/sdb

grub /dev/sdb
root (hd1)
setup (hd1,0)

Finally, reboot once and make sure that everything works as expected.

The system is now running with one old drive and one new drive. The next step is to perform the same steps with removing the other old drive and rebuilding and re-adding it to the raid system. The steps are the same as above, except performing them with /dev/sda. I also had to change my BIOS to boot from the second drive.

Once both drives are installed and working with the RAID array, the final part of the process is to increase the size of the file system to the full size of our new drives. I first had to disable the EXT3 file system journal. This was necessary so that the online resize doesn’t run out of memory.

Edit /etc/fstab and change the file system type to ext2, and the arguments to include “noload” which will disable the file system journal. My /etc/fstab looks like this:

# /etc/fstab: static file system information.
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
proc            /proc           proc    defaults        0       0
# /dev/md1
UUID=b165f4be-a705-4479-b830-b0c6ee77b730 /               ext2    noload,relatime,errors=remount-ro 0       1
# /dev/md0
UUID=30430fe0-919d-4ea6-b3c2-5e3564344917 /boot           ext3    relatime        0       2
# /dev/sda5
UUID=94b03944-d215-4882-b0e0-dab3a8c50480 none            swap    sw              0       0
# /dev/sdb5
UUID=ebb381ae-e1bb-4918-94ec-c26e388bb539 none            swap    sw              0       0

You then have to run `mkinitramfs` to rebuild the initramfs file to include the desired change to the mount options

root@host:~# mkinitramfs -o /boot/initrd.img-2.6.31-20-generic 2.6.31-20-generic

Reboot to have the system running with journaling disabled on the root partition. Finally, you can actually increase the RAID device to the full size of the device:

root@host:~# mdadm --grow /dev/md3 --size=max

And then resize the file system:

root@host:~# resize2fs /dev/md1
resize2fs 1.41.9 (22-Aug-2009)
Filesystem at /dev/md1 is mounted on /; on-line resizing required
old desc_blocks = 38, new_desc_blocks = 117
Performing an on-line resize of /dev/md1 to 488084800 (4k) blocks.

The system is now up and running with larger drives :) . Change the /etc/fstab, rebuild the initramfs, and reboot one more time to re-enable journaling and be running officially.

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  1. Glenn said,

    on August 29th, 2011 at 12:57 am

    This is pretty similar to what I’ve done in the past. I didn’t know about the journalling tip, thanks for that.

    I like the watch command, but you may want to use the -n30 delay (or some other largish number) option with that to reduce the polling frequency, especially if you are pushing priority to the array rebuild. Hitting /proc/mdstat seems to be a bit heavy in terms of system calls.

    One other thing I’d also suggest, is instead of running the resize on a live filesystem, bootup with a livecd such as finnix. That will allow you to run fsck directly before resize2fs, as newer versions seem to enforce. And to be working with an offline filesystem, rather than a live one.

    Very nice writeup.

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