Raid 5 hardware questions

Discussion in 'Mac Pro' started by ScientistRyan, Oct 12, 2010.

  1. macrumors newbie

    Joined:
    Jul 23, 2010
    #1
    Hey all. I currently have a 4 bay drobo with 1.5TB drives for use with time machine backups. The drobo is a real piece of crap in my opinion with its constantly loud fan, ability to make my mac pro drop its USB bus until it is rebooted(having to use the command line as the USB keyboard and mice don't work), and the fact that it has decided to erase itself twice in the last few years. Plus its all proprietary and the drobo support is lacking.

    With this said I want to go to a raid 5 setup for my time machine backups. As for my mac pro it is a 2009 octo if it matters. What I have found hardware wise is the following:

    Controller: http://eshop.macsales.com/item/Newer Technology/MXPCIE6GRS/
    Enclosure: http://www.newegg.com/Product/Product.aspx?Item=N82E16816132016
    Drives: 8 Samsung 5900RPM 1.5TB drives

    Will all of this work so I can setup a RAID 5 with all 8 drives?? Can anyone estimate what read/write speeds I may get with this setup? Should I find a different controller? I want a controller that is under $250 if the one I listed wont work.

    Any insight from the RAID gurus here would be great! THANKS
     
  2. macrumors G4

    Joined:
    May 6, 2008
    #2
    1. That card uses a software implementation for RAID, not hardware. So it's not capable of handling it properly (can't deal with the write hole issue). It will be fine for 0/1/10 or JBOD, nothing else.

    2. You won't get a hardware card for $250.

    What you can get, is an enclosure that has an RoC (RAID on a Chip) inside that can deal with the write hole issue, as it is a hardware controller (inexpensive, but it's hardware).

    The Qx2 from OWC is such a unit, and it's $300USD, but only holds 4x disks, so you'd need 2x, and run 2x separate arrays.

    Past that, and you're looking at $1000 before drives (card for ~$600 and enclosure for $400).
     
  3. thread starter macrumors newbie

    Joined:
    Jul 23, 2010
    #3
  4. macrumors G4

    Joined:
    May 6, 2008
    #4
    The Newertech RAID card uses software to implement all the levels it's rated for, not hardware. It's nothing more than an eSATA card with PM support and drivers, which contain the RAID support. So it has to use system resources to actually do the processing.

    Now what you need to understand is, that software is fine for 0/1/10 and JBOD, but not parity based arrays (5/6 or nested parity 50/60). Even if it states a parity array (level 5 is as high as they go with software implementations), as it cannot deal with the write hole issue (it requires a hardware solution, which only exists on proper hardware RAID controllers; uses a separate processor, and usually has a cache).

    I really can't stress this enough; do not use a software implementation for a level 5 array. You're begging for trouble in the form of corrupted data (not if, but when).

    For further information, I'd recommend reading the RAID Wiki (last line of this ssub-section is a description of the write hole).
     
  5. macrumors 6502a

    Joined:
    Apr 18, 2008
    #5
  6. thread starter macrumors newbie

    Joined:
    Jul 23, 2010
    #6
  7. macrumors 6502a

    Joined:
    Apr 18, 2008
    #7
    yeah pretty sure :)
    check the sansdigital site to double check ;) its 3am my mind is fried exporting some jpgs then back to work got behind this week :)

    so truly cross eyed of doing PS and raw work for the last 3 days straight :)
     

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