RUNNING 128gb x 2 SSDs in raid and getting only 28mbps write speed - WTF?

Discussion in 'Mac Basics and Help' started by gochi, Feb 15, 2014.

  1. gochi macrumors 6502

    Joined:
    Mar 31, 2011
    #1
    Please check the screens below - this makes no sense.

    Using 2x micron realssd SATA III- advertised speeds at about 300mb/s READ and 150mb/s WRITE.

    Yet according to xbench, i am getting 250 mbps/read and 18mbps/write.

    Now assuming if i was using each one separately the read speed would be fine, but since i have them in raid the read speed should be higher and the PATHETIC write speed should be about 50x faster.

    http://i62.tinypic.com/250mdtt.png
     
  2. Intell macrumors P6

    Intell

    Joined:
    Jan 24, 2010
    Location:
    Inside
    #2
    Try something other than Xbench. It's rather old and it's very possible that it is giving you skewed numbers.
     
  3. gochi thread starter macrumors 6502

    Joined:
    Mar 31, 2011
    #3
    i tried black magic and got comparable results. someones gotta know whats up.

    ----------

    just ran a drivers diagnosis and I'm getting 100% ssd health.
     
  4. Jedi Master macrumors regular

    Joined:
    Apr 5, 2013
    Location:
    ar the moment on the Death Star
    #4
    What type of raid and is it a hardware or software raid

    The lack of information only allows for a WAG.
     
  5. gochi thread starter macrumors 6502

    Joined:
    Mar 31, 2011
    #5
    stripped raid set; hardware i suppose, not sure what you mean by software.


    its crucial c300 sata3 and i can't upgrade the firmware.
     
  6. tuna macrumors 6502

    Joined:
    Apr 11, 2010
    #6
    RAID is very old technology. It has always been a bag of hurt. Now we have object-based storage strategies that are more reliable than RAID. Even striping for pure speed has become redundant. Within any single SSD the architecture is already highly parallel effectively striping the data across the SSD's many individual flash chips.

    I would recommend nixing the RAID and seeing how it goes. If you want more speed there are already affordable SSDs that will completely soak up an entire SATA3 channel without needing RAID.

    RAID was always overrated for consumer and "prosumer" applications where PC enthusiast magazine articles about "quadrupling" their data speeds by striping four drives, for example. In reality I have never heard of someone with a RAID who didn't eventually come around to thinking that it was a pain in the ass.
     
  7. chown33 macrumors 604

    Joined:
    Aug 9, 2009
    #7
    Disk Utility can treat multiple external drives as a RAID set:
    http://support.apple.com/kb/ph5834

    For example, if two ordinary disk drives are connected via USB, they can be configured as a RAID 0 set. Other choices are possible.
     
  8. Tumbleweed666 macrumors 68000

    Joined:
    Mar 20, 2009
    Location:
    Near London, UK.
    #8
    I agree I don't see any point in using RAID across SSDs. Disks, maybe. SSD, why woudl you do it? Its nota s if you need to wait for the heads to come around again or can interleave other writes whilst heads move :D

    Basically it makes the whole setup more unreliable, and is bound to decrease speed.

    I wonder if the disk driver implementing RAID is the bottleneck?

    Whatever, undo it.
     
  9. glenthompson macrumors 68000

    glenthompson

    Joined:
    Apr 27, 2011
    Location:
    Virginia
    #9
    Since the read is about what you can expect but the write is slow, I suspect the raid implementation. Reads only require accessing one drive but writes require writing to both. It may be writing to one, verifying the write then writing to the other. Hard to say without more hardware and software specifics.
     

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