Whats better RAID-0+1 or RAID-5 - Veritas Volume Manager

This is a discussion on Whats better RAID-0+1 or RAID-5 - Veritas Volume Manager ; Hi I've got to spec a system for a very large database. My initial thoughts were to spec it with RAID-5 being used on the arrays to provide redundancy. However, after reading the requirements I find that online access and ...

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Thread: Whats better RAID-0+1 or RAID-5

  1. Whats better RAID-0+1 or RAID-5

    Hi

    I've got to spec a system for a very large database. My initial thoughts
    were to spec it with RAID-5 being used on the arrays to provide redundancy.
    However, after reading the requirements I find that online access and
    maximum availablility is being given great importance. With this in mind I
    thought it would be better to go for striping and mirroring (RAID-0+1) to
    maintain system availability in the event of a single disk failure.

    Am I right in thinking that RAID-5, although providing data redundancy
    through parity logging, requires that in the event of a failure the failing
    volume must be taken offline to allow it to be rebuilt.

    All help gratefully received

    JJ




  2. Re: Whats better RAID-0+1 or RAID-5

    >>>>> "John" == John Martin writes:

    > Hi I've got to spec a system for a very large database. My initial
    > thoughts were to spec it with RAID-5 being used on the arrays to
    > provide redundancy.


    RAID5 in software is not fun. You only want to use it for applications
    where writes are relatively rare. No database I know of fits that
    description. If you want RAID5, go buy a disk array that can do it in
    firmware.

    > However, after reading the requirements I find that online access
    > and maximum availablility is being given great importance.


    Not performance?

    > With this in mind I thought it would be better to go for striping
    > and mirroring (RAID-0+1) to maintain system availability in the
    > event of a single disk failure.


    striped-mirror volumes are more robust than RAID5 volumes, simple
    because they have a greater degree of redundancy. They also have much
    better performance. The drawback is that you lose a greater proportion
    of the raw disk. If that's not a problem (and it shouldn't be, with
    today's prices of raw disks), stripe-mirror is definitely the way to go.

    > Am I right in thinking that RAID-5, although providing data
    > redundancy through parity logging, requires that in the event of a
    > failure the failing volume must be taken offline to allow it to be
    > rebuilt.


    No, VxVM will rebuild on the fly (provided it's got a spare disk to
    use instead of the failing one, of course).
    --
    Calle Dybedahl, Vasav. 82, S-175 32 Jaerfaella,SWEDEN | calle@lysator.liu.se

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