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RAID Levels - Best Practice and Performance?

    Question

  • Assuming storage space is not an issue and the requirement for best recoverability. What is the best practice and best performance RAID configuration for Hyper-v VMs? Please ignore pass-through disks for this scenario, I'm talking about vhd file placement.

    For example, 1 host with 8 VMs and no connection bottlenecks - which would you choose and why:

    1 x Large RAID 10 or RAID 01 set (all VMs striped across same RAID set)
    1 x Large RAID 5/6 set (all VMs striped across same RAID set)
    8 x RAID 1 sets (1 for each VM)
    Mutliple RAID 10 or RAID 01 sets
    Multiple RAID 5/6 sets
    Multiple RAID 1 sets

    Any others?

    I purposely haven't mentioned RAID 0 due to the recoverability requirement.

    Thursday, October 21, 2010 8:08 AM

Answers

  • Hi,

    I tested RAID 5 before in big implementation and it went fine from IO perspective (Hosting Exchange Hub, CAS VMs ). RAID5 is generally an cost effective solution and cheap.

    See http://sqlblog.com/blogs/linchi_shea/archive/2007/02/07/is-raid-5-really-that-bad.aspx  for a point of view suggesting RAID 5 may not be so bad. Be sure to read the responses. Notice that most people seem to be against RAID 5. Also notice that Linchi's post is referenced in this post http://weblogs.sqlteam.com/billg/archive/2007/06/18/RAID-10-vs.-RAID-5-Performance.aspx  which also has a good discussion suggesting the standard "it depends" IT answer may apply.

    RAID 10 is still an option You'll get the good performance and protection for your VMs.  Check out this blog post.  http://blog.concurrency.com/2010/06/09/what-disk-type-do-i-use-with-hyper-v-r2/

     

    Sourcehttp://social.technet.microsoft.com/Forums/en-US/winserverhyperv/thread/9649dd7f-33f6-4626-91c5-fee67d9497fc/

    "some guidelines from my personal objective:

    2x300GB RAID1 => OS (I knew 300GB for OS is a much, but RAID1 is generally recommended for OS)

    +

    6x300GB

    RAID1+0 -> If you have the "luxury" to loose the half of capacity that would be in my eyes the "fastest" solution here but "only" round about ~ 900GB netto available

    RAID5 -> an RAID5 is in general (if all data is written to disk :-)) also fast in the reads, but if many data will be written/changed a.e. Exchange or SQL, you loose much performance due to the required well known parity calculation :-(

    RAID5+0 (if available) -> an RAID50 can also be an solution here, where you need at min. 6 disks and which would be the case here. RAID 5+0 is in general 2 x an RAID5 + an RAID0 on top of it :-) therefore you have theoretically the double performance of an "normal" RAID5"

    Thursday, October 21, 2010 4:56 PM
  • Hello,

    I typically go with RAID 10 because of the performance and recoverability benefits.  This is especially true when talking about a one server implementation with local disk.  For example, RAID 10 can sustain the loss of several drivers and has a less significant degraded / rebuild performance hit than RAID 5.  Certainly RAID 5 can fit certain implementation needs, but given the choice I'd go with RAID 10 if your capacity needs are met.

    Nathan Lasnoski


    http://blog.concurrency.com/author/nlasnoski/
    Friday, October 22, 2010 3:19 AM

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