Mac pro non-paired drives RAID 0 array

Discussion in 'Mac Pro' started by OracleRedux, Oct 9, 2010.

  1. OracleRedux macrumors member

    Nov 21, 2008
    Guildford, UK
    I currently have the following drives in my Mac Pro (Early 2008):
    Samsung HD203WI

    The Caviar Blue drives were bought in the pre-Black era, back in Early 2008. Or at least they certainly hope so; I purchased the WD6400AAKS as the boot drive thinking it was the fastest 7K available at the time (BareFeats review).

    I am about to install either an OCZ Vertex 2 or OWC Mercury Extreme Pro SSD in the optical drive bay.

    I plan to re-purpose the 640, and either the 750 or 500, as a Software RAID 0 array (using Disk Utility), backed up using Time Machine / Super Duper. The third WD drive will be used for Boot Camp. The Samsung is a "green" Media Drive (although AJA has it currently matching the WD 640 in speed).
    My intention is to improve the speed of access to user files etc, since a 60GB SSD is not big enough, nor suitable for my home folder.

    I therefore ask; am I nuts? (I am aware of the increased risk of data loss)

    My initial thought is that mismatched drives in a RAID 0 array may not result in the performance increase I am looking for. Apologies for the capitalisation error in the post title - wish I could edit it!
  2. nanofrog macrumors G4

    May 6, 2008
    Yes, you can stripe mismatched drives. :)

    What will happen, is both the speed and capacity will be affected by the smallest and slowest drive respectively in the set. So if you've a 500 and 750GB member, you'd get 2x 500GB = 1TB of usable capacity (additional 250GB on the 750 won't be accessible, unless you partition it in a 500/250 scheme, as you'd want the faster tracks for the stripe set).

    Worst case performance will be n members * the slowest disk (likely what you'll see, as it's only a 2 member set, and the performance difference between the intended disks isn't likely to be that much, say a differential of 10MB/s or so).

    So if the slowest drive is good for ~75MB/s, then 150MB/s is a realistic estimate of sustained throughputs (respective of read/write values you can locate from independent reviews).

    Hope this helps. :)
  3. DoFoT9 macrumors P6


    Jun 11, 2007
    as per the scenario nano has outlined - you could use the remaining space to JBOD (or similar) it into a nice extra partition to muck around with :)

    i have done something similar with my 4 drive RAID5 array.

    so a striped RAID in your scenario would give 1.5TB total, and a 140GB + 250GB partition remaining - JBOD that into a 390GB extra partition and away you go!
  4. OracleRedux thread starter macrumors member

    Nov 21, 2008
    Guildford, UK
    Thanks very much for both those replies, encouraging. To clear up any ambiguity; I only plan to stripe 2 drives. The third will be used for Windows under Boot Camp and as I understand it, one cannot have RAID on a Boot Camp drive.

    How much of a performance hit does *software* RAID result in?
  5. Transporteur macrumors 68030

    Nov 30, 2008
    Pretty close to n-times the performance of a single drive, with n being the amount of drives you put in a RAID 0 array.

    This won't apply for access time and random access, though, only for sequential access.

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