RAID question

Discussion in 'Mac Pro' started by thermodynamic, Feb 14, 2010.

  1. thermodynamic Suspended

    thermodynamic

    Joined:
    May 3, 2009
    Location:
    USA
    #1
    On my 2009 Mac Pro, OS X's disk utility seems to allow the provision of making a mirror RAID or a stripe RAID.

    Is it possible to shove in 2 drives, make a RAID 0 for two of them, and then add in 2 more drives to make a RAID 1 out of that RAID 0? (a RAID 0+1??)

    Thx!
     
  2. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #2
    Yep. I'd go 10 (1 + 0) though, as it's a little safer. :)
     
  3. acluett89 macrumors newbie

    Joined:
    Feb 13, 2010
    #3
    With respect to the tradeoff between redundancy vs. data protection, what recommendations can you make on RAID levels? Is it completely dependent on the environment, or are there clear advantages to using a RAID 5 over RAID 3, etc.?
     
  4. surflordca macrumors 6502a

    surflordca

    Joined:
    Nov 16, 2007
    Location:
    Ontario, Canada
    #4
  5. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #5
    Redundancy = data protection = availability = operational uptime - think 24/7 operation. The premise is, if a drive drops out, it will still run (i.e. RAID 5). But if a second drive goes, the array is lost, and the system is "broken", and needs the array rebuilt and restored from backups. Other levels (i.e. 10 or 6) allows for 2 drives to fail, and still remain operational (though once a disk fails in a redundant array, it's performance is degraded). In such a case, it takes a 3rd drive failure to trash the system.

    RAID levels not only deal with redundancy, but have performance penalties as well as capacity differences. For example, in a level 10 array, you get 2 drive redundancy (4x disks total), but at the cost of only being able to use half of the capacity (it's performance is decent).

    So the compromise consists of redundancy, performance, and usable capacity.

    I'd recommend reading the RAID wiki page to get an understanding of what each level does. Also pay attention to the write hole issue associated with parity based arrays (5/6/50/60), as only a proper RAID card (processor + cache) should be used, as it has a solution that deals with it (NVRAM).
     
  6. student_trap macrumors 68000

    student_trap

    Joined:
    Mar 14, 2005
    Location:
    'Ol Smokey, UK
    #6
    is it possible to have 2 x 500GB drives set up in a raid 0, and then have a third 1 TB drive (rather than two more 500 GB drives) to constantly back up the raid?
     
  7. Transporteur macrumors 68030

    Joined:
    Nov 30, 2008
    Location:
    UK
    #7
    Only with an appropriate sync program/script such like rsync, since there is no RAID setup that would work that way.
     
  8. student_trap macrumors 68000

    student_trap

    Joined:
    Mar 14, 2005
    Location:
    'Ol Smokey, UK
    #8
    thanks for letting me know
     
  9. tomllama macrumors regular

    Joined:
    Jan 7, 2007
    Location:
    CA
    #9
    One thing to remember is that you can do RAID 0, 1 or 10 in software with just disk utility. RAID 5, 6 or other 'flavors' require a real RAID card which means a significant expense for the card and usually for enterprise class drives (instead of the cheaper consumer drives).
     
  10. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #10
    You have to be careful though, a there are Fake RAID controllers out there that claim to support RAID 5. They're software based however, and do NOT have the ability to handle the write hole issues.

    The same goes for some RAID-in-a-Box solutions as well (i.e. Drobo type devices) that use a small computer board and store an OS on Flash ROM, say based on an Intel Atom in the enclosure, and is a software solution (assuming it uses standard levels, it can't handle the write hole either). There are some propreitary levels as well (i.e. product specific) that have to be researched in detail to be sure as to what's going on with it to be sure it's safe. I'm not a big fan of such proprietary devices, as there may not be enough information to be sure prior to purchasing the device and thoroughly test it out.
     
  11. sailmac macrumors 6502

    sailmac

    Joined:
    Jan 15, 2008
    #11
    FWIW, I have such a setup running. From a user perspective the RAID0 volume looks just like any other.

    I have SuperDuper scheduled nightly to update a bootble clone of the RAID0 startup volume.

    I compliment this with Time Machine backups to another drive.

    For my needs, this backup scheme is a reasonable approach for managing the risk of using software RAID0 as a boot volume.
     

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