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Linux software Raid 5 - my experience

  • 23-11-2007 1:55pm
    #1
    Khannie
    Registered Users, Registered Users 2 Posts: 37,485 ✭✭✭✭


    Well....I just finished building my raid 5 array there last night. It's made up of 3 x 750G hitachi hdd's.

    Original config was:
    2 x 200G samsungs and 1 x 320G seagate in LVM. This was running out of space and the 3 x single points of failure = nervous Khannie, so I decided to go with the software raid 5 built into the linux kernel (for a variety of reasons, not least of which was the lack of manufacturer lock in).

    So I followed this guide on the gentoo wiki (great resource).

    Basically I copied all of the data from the LVM onto a single 750G drive (drive A), then set up a broken raid 5 array (i.e. running with 2 disks out of 3...drives B and C), copied over from the 750G drive to the new 1.5TB raid 5 array (drives B and C), verified that the data was good, then added the first 750G drive (Drive A) to the array (wiping its contents, but adding the redundancy). Presto! Migration complete. (The migration takes a long time mind you. Averaged around 50MB/s.)

    Then...

    and this is the good bit....

    I ran a speed test with hdparm.....

    164MB/s!!!!!!!!!!!!!!!!

    I thought it was lying, so I did:
    time cat <largefile> > /dev/null
    and found out that it was actually running at around 150MB/s. Super super impressed.

    I went with XFS for the filesystem. I'd read good things about it and I'm not disappointed. Deletes are very fast.

    Edit: I should point out that there is a computational overhead associated with writing to the disk (to create the parity blocks) so heavy disk usage = CPU overhead. I have a quad core, so this isn't an issue for me, but it's worth bearing in mind.


Comments

  • #2
    niallb
    Registered Users, Registered Users 2 Posts: 2,750 ✭✭✭niallb


    Nice report.
    Thanks for the figures.


  • #3
    Khannie
    Registered Users, Registered Users 2 Posts: 37,485 ✭✭✭✭Khannie


    No worries. :)

    99% sure I'm gonna use the 2 x 200G samsung P120's in raid 1 as the OS drive. They should be pretty nippy too, but not as fast.


  • #4
    SouperComputer
    Registered Users, Registered Users 2 Posts: 6,949 ✭✭✭SouperComputer


    refresh my memory on what Distro/kernel you are using again? Did you set it up thru a GUI or command line?

    I want to doe a single NAS in the new house, and the prices for the HD enclousures are nothing short of a joke.


  • #5
    Khannie
    Registered Users, Registered Users 2 Posts: 37,485 ✭✭✭✭Khannie


    I'm using gentoo. I set it up through the command line, but it was very straightforward. The guide I linked to should work for any distro (except for the software installation commands). For a file server, I'd say centos server would be just lovely.


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