Add disks to existing RAID 1

Posted on 2006-06-04
Last Modified: 2010-04-03
I need to increase the available storage on a server. The server has performed without fault for a couple of years, so I don't want to screw it up! I need to keep redundancy.

DELL Poweredge 2600 (Service Tag: HG06W0J)
PERC 4i Raid
2 x 36GB SCSI Drives, giving me around 30GB available storage (25GB used)
Redhat Linux 9
RAID 1 config (hardware)

I was planning on purchasing a further 2 x 36 GB SCSI drives.

From the Dell docs, it seems to me that this should be possible.
However, I absolutely DO NOT want to have to reinstall the OS.

I would like to hear from someone who has done this (I can search for docs myself).
Any gotchas appreciated.
How long is the server likely to be offline (25GB used)?
Should I take an image using Acronis or similar (would rather not, because it adds to the time taken)?
Many thanks
Question by:mikefish
    LVL 15

    Accepted Solution

    The quickest and safest way to increase the storage is to put the 2 new disks in and configure them as a new RAID 1 set, create one or more partitions on it and mount them. You don't need to touch the existing RAID set.

    If you decide to add the new disks to the existing disks to create a RAID 5 or RAID 10 set, you absolutely must take an image first using Acronis or similar (you've got Linux, so you can use dd). Otherwise your going to pull your hair out if anything goes wrong.
    LVL 34

    Assisted Solution

    First and formost before any hardware change in a server take a backup. The two best options were mentioned above either creating a new raid 1 on the 2 new drives, which will have minimal down time but only add another 36GBs of storage, or to reconstruct the array to a raid 5 giving you 72 GBs of extra storge. The reconstruct option does have a possibility of data loss to minimize that chance you would want absolutly no one accessing the server during the rebuild (disconnect from the network is the best way to ensure this) and do not restart the system. The reconstruct would take about 3-4 hrs.

    Author Comment

    Many thanks to you both.
    Rebuilding the RAID seems the "proper" thing to do (hate wasting storage), however, it sounds like it would be much simpler and quicker adding a new RAID 1 set. The extra 36gb storage will be enough.
    Once I've configured the new RAID in the bios, are there any differences linux-side for adding the new disk compared to adding a non-raid disk?
    LVL 87

    Assisted Solution

    It is a lot easier and more failsafe to use just another raid1 array. Maybe you could use  larger disks than the 36GB ones (these might even be difficult to get these days). Just make sure you have room inside the case for the extra HD's. As linux will use the same driver modules getting the new array to run in that OS shouldn't be much of a problem, you'll mainly just have to fdisk the new array then add it to your /etc/fstab file. It'll look similar to your current array.

    Author Comment

    Good point re larger disks. If it's a separate array, then I guess the disks don't have to be the same size.
    LVL 87

    Expert Comment


    Author Comment

    thanks for your help everybody.

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