What is a RAID "stripe size"

Discussion in 'Mac Pro' started by AppleWorking, May 26, 2009.

  1. AppleWorking macrumors regular

    Joined:
    Jan 20, 2009
    #1
    I want to RAID 0 two WD 640 Blacks...

    I have never setup a RAID before and this question may be stupid, but do I need to specify a "stripe size" when I set it up?

    If I should specify a size, where do I do this, what size should I specify, and how do you do it? :)

    Thanks
     
  2. VirtualRain macrumors 603

    VirtualRain

    Joined:
    Aug 1, 2008
    Location:
    Vancouver, BC
    #3
    In a nut-shell, a RAID0 array is a striped set of disks, so setting a stripe size is necessary but the default of 64K (I think) is the best balance for magnetic disks in most cases. Smaller stripe sizes increase performance from added parallelism but suffer from decreased performance from added seeks. Larger stripe sizes decrease performance from reduced parallelism but increase peformance from reduced seeks. Smaller stripes generally work better for small files and larger stripes for larger files with 64K being a good balance for most OS activites. If you are using the striped array primarily for large media files, you might want to consider a 128K stripe.

    For SSD's it's another matter... http://forums.macrumors.com/showthread.php?t=705783

    What is a stripe? In simplest terms it's the amount of data written to each drive before switching to the next drive. Thus if you have a 64K stripe size and you write 256K to disk, you will write the first 64K to the first disk, the second 64K to the second disk, the next 64K to the first disk, and the last 64K to the second disk. Thus you can see by splitting up the write operation across the two drives like this, you should get nearly double the performance but if one of the drives fails, it takes all your data with it.
     
  3. AppleWorking thread starter macrumors regular

    Joined:
    Jan 20, 2009
    #4
    Hey thanks, that's the information I was looking for...

    So if I setup a software RAID with two WD 640 blacks using Leopard it will automatically default to 64K? So I shouldn't even worry about it since it will be setup to the optimal size in the background? Is this correct?

    Is there a utility app I should use instead of disk utility?

    Thanks
     
  4. VirtualRain macrumors 603

    VirtualRain

    Joined:
    Aug 1, 2008
    Location:
    Vancouver, BC
    #5
    When you setup your RAID array with Disk Utility, you can click an "Options" button if I recall correctly and see the default stripe size and change it there if you desire.
     

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