RAID speed dropped for some reason..

Discussion in 'Mac Pro' started by ajfrankla, Aug 19, 2012.

  1. ajfrankla macrumors newbie

    Aug 19, 2012
    Hong Kong
    Hey Guys,

    A while ago when I did a Disk Speed Test, I was getting 260-270 MB/s. After recently realising that my DaVinci Resolve performance dropped slightly, I decided to do another Disk Speed Test of which I then found out disk performance dropped to 150-160 MB/s.

    I then decided to delete some unnecessary files from my RAID to increase available space, thinking performance could improve as a result. However, I was still getting 150-160MB/s.. :(

    I checked my RAID Utility and it still has a green light and says 'Good' on the two volumes I have. The last time the Battery conditioned itself was about two and a half months ago.

    What else can I do to get back to 260-270 MB/s again?

    Also... and whats strange... I did another test on my Mac HD volume at RAID5 and was getting almost 300mbs as opposed to my other volume (currently 150mbs. 260mbs before....). Im really confused...

    I have x4 WD black caviar HDs (1TB each) and Apple RAID card.

    Any help is appreciated :)

  2. nanofrog macrumors G4

    May 6, 2008
    Not sure what the pre-deletion capacity was, but once you're over the 50% mark, things will slow down drastically, due to data is stored on the inner tracks of the platters (less data transferred per rotation).

    Even after deletion, any data that was stored on those inner tracks is still there.

    To fix it, backup the array, delete the data on the array, then restore it from the backup (gets the data on the outer-most tracks, thus increasing throughputs).

    Another thing to watch with that particular card, is the battery. Once it no longer stores a sufficient charge, the card throttles the speed (essentially runs as if the set were degraded).

    Not sure if this is a RAID 5 as you didn't give the specific level of the volume in question, but make sure the disks are all good as well (verify the set isn't running in a degraded state).

    Without additional information, I'm under the impression from what you did provide, that your data is likely stored on inner tracks, so give that solution a try.

    Hope this helps. :)
  3. ajfrankla thread starter macrumors newbie

    Aug 19, 2012
    Hong Kong
    Thank you for the reply.

    After backing up all data onto an external and deleting that data from the slow volume, should I do anything in the Disk Repair utility? or is just deleting everything with a simple click enough?

    Whats really confusing me, is why my two volumes set at RAID5 coming from the exact same hardware (x4 WD black caviar HDs + Apple Raid card) is now functioning different speeds.. technically shouldn't they be running at identical speeds like before?

    Thanks again.
  4. Dominic49 macrumors newbie

    Jan 15, 2012
    the utility will tell you when the battery goes dead but they are only ~30 last time I had to order a set from apple.
  5. nanofrog macrumors G4

    May 6, 2008
    Did you partition the drives, then create arrays out of different partitions?

    Assuming you did this, the second partition on each drive is slower, as it's using inner tracks. Another thing to consider, is an array's speed is governed by the slowest disk/partition. Worse yet, is if you're trying to access both arrays (same disks via partitions) simultaneously, as it's the same hardware (heads have to move a lot more, which is both slower, and adds additional stress to the drives used).

    So it's not a good idea to split drives when using RAID regarding speed, unless the partition using the inner tracks isn't used, or isn't speed critical, nor are multiple arrays on the same disks being accessed simultaneously.

    As per your question, deleting the existing data is usually sufficient, but if possible, I'd delete the entire array, re-create it, then restore the data.

    Another note, Caviar Blacks aren't really sufficient for running a hardware based RAID array (RAID card), as the firmware is insufficient for the task (recovery timings programmed into the firmware aren't written with RAID cards in mind). You're living dangerously by using consumer grade HDD's, which is what the Caviar Black series are.

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