Raid 5 3 disks rebuilding

Posted on 2014-08-13
Last Modified: 2014-08-18
Hi all,

We have recently ordered x2 1TB new hot swap disks for a HP server.
The server in question is currently running x3 500Gb disks in RAID 5 Array.

My question is would we be able to swap out 1 500Gb for one of the new 1TB, wait for the other disks to rebuild onto the 1TB and then do the same with the other 1TB?

Any advice appreciated,

Many Thanks

Question by:Techdivision
    LVL 10

    Expert Comment

    You should be able to, although you should be aware that during the rebuild there is increase risk to the array failing if any other disk fails.  Therefore I would make a full backup first (to a destination not part of the array) if at all possible.

    You also should check your manual to see if there is any particular warnings.

    Finally, this will not increase the size of the array.  Your array will only use 500GB from the 1TB until all 3 disks are upgraded to the larger size.
    LVL 46

    Expert Comment

    I would ask - what is the purpose of doing this?
    You are going to trash 500GB of usable space if you keep one 500GB HDD there and replace two only.
    Better if you get three 1TB drives - take full backup of your current configuration and then rebuild RAID with new drives - perform restore.
    LVL 87

    Expert Comment

    It is rather dangerous to do it that way, as the rebuild can kill your array, and even if it works, it will take a lot of time (during which your data is at risk, and the server runs slowly). Besides, after having replaced all the disks you'd still have to expand the array (or create a separate volume for your added space), and such things can always fail or not be supported by your controller.

    It is far better and safer to backup, remove the old disks, insert the new ones, create the new array(s) and restore.

    Also make sure the disks you bought are certified by HP to work for your server, and have the correct firmware. They need to be enterprise class disks.

    Author Comment

    The disks are genuine, thanks for all the advice.

    @noxcho sorry I failed to mention that the customer I believe can only afford 2 disks at the moment because they're about £200 + per disk.

    We will probably go for the restore option, I just needed to know if it was possible.

    Many Thanks for the help

    I will let you guys know how it goes.
    LVL 46

    Accepted Solution

    Yes, it is possible. But really it makes no sense (could make sense only if 500GB drives are failing) to use 1TB two drives in set with 1x500GB drive. Try to tell it to the customer, maybe they find budget for third one as well.

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