Intel X25 G2 - massive drop in read performance

Discussion in 'MacBook Pro' started by Mueslimonster, Feb 9, 2012.

  1. Mueslimonster macrumors newbie

    Joined:
    Jul 7, 2008
    Location:
    Germany
    #1
    I installed an Intel X25m G2 in my MacBook Pro (unibody) some time ago. Worked like a charm. When the patch to enable Trim support on Leopard came out, I applied that and subjectively felt an increase in performance.

    Last year in October I switched to Lion and lost the patch again. A couple of weeks ago I had the feeling that my Mac had become a bit sluggish (boot performance, application start-up etc), so when the new Trim patch for Lion came out I happily applied that as well, thinking that this would counter the performance loss.

    However, little changed. I did an XBench a couple of times and get these results:


    Sequential 104.63
    Uncached Write 182.67 112.16 MB/sec [4K blocks]
    Uncached Write 119.48 67.60 MB/sec [256K blocks]
    Uncached Read 49.08 14.36 MB/sec [4K blocks]
    Uncached Read 249.15 125.22 MB/sec [256K blocks]

    Random 458.33
    Uncached Write 769.50 81.46 MB/sec [4K blocks]
    Uncached Write 204.17 65.36 MB/sec [256K blocks]
    Uncached Read 1194.49 8.46 MB/sec [4K blocks]
    Uncached Read 590.77 109.62 MB/sec [256K blocks]

    What is going on? Does anyone have an idea why my read performance dropped so badly? It used to be around 190-200 MB/sec. I know that SSDs degrade over time, but I thought that was only related to write performance. I have the 120Gb version and 28Gb free space.
     
  2. maflynn Moderator

    maflynn

    Staff Member

    Joined:
    May 3, 2009
    Location:
    Boston
    #2
    Enabling TRIM means that the OS tells the drive when a delete is occurring so it can mark it as such, instead of the SSD not knowing and performing two operations when its not marked empty.

    Applying it will no help you on prior delete cycles by default. That is if you used the drive without TRIM for months and months and now enabled it. Trim will help moving forward on data blocks marked as deleted but you need to do something like do a erase free space (found in the disk utility) to handle the other stuff that TRIM didn't know about since it wasn't enabled
     
  3. Mueslimonster thread starter macrumors newbie

    Joined:
    Jul 7, 2008
    Location:
    Germany
    #3
    I already erased free space using disk utility, but to no avail. However, this should only affect write performance, right? It's the read performance I'm worried about. Any idea?
     
  4. maflynn Moderator

    maflynn

    Staff Member

    Joined:
    May 3, 2009
    Location:
    Boston
    #4
    Bummers, I thought that might have been the case :(
     
  5. Mueslimonster thread starter macrumors newbie

    Joined:
    Jul 7, 2008
    Location:
    Germany
    #5
    For anyone interested - I found the culprit for the massive slow-down.

    It was Lion's disk encryption. Be aware that turning on this feature may slow down your maximum disk performance by almost 40%- at least in the Xbench test. I'm not sure how this translates into real life performance, but ever since I turned disk encryption off again, my system has become way more responsive again (boot-up time etc).
     
  6. alphaod macrumors Core

    alphaod

    Joined:
    Feb 9, 2008
    Location:
    NYC
    #6
    Also erasing it via Disk Utility (including using zeroing) does nothing to actually zero the drive due to write wearing algorithms. If you want to truly zero out your disk, you need to perform a secure erase. There are utilities to do this and the procedures takes maybe 10 seconds to complete.
     

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