Looking for advice for RAID array for 4(+) x Intel 520

Discussion in 'Mac Pro' started by percival504, May 3, 2012.

  1. percival504 macrumors regular

    Feb 10, 2009
    Hello all.

    I am currently using the following: 4 x Intel 520, 3 x 1 TB WD Caviar Black and 1 x 2 TB WD caviar Black. I also have an original RevoDrive (which worked fine) but its gathering dust.

    I want to do RAID 1 or RAID 10 with the 4 SSD and may a RAID 1 with some of the Caviar Blacks. I was going to get a hardware RAID card (ATTO or Areca), but I am wondering whether I actually need it. Since I read Nanofrog's posts stating that MLCs are useless for parity, it seems like only RAID 1, 10 or 0 are possible anyway.

    Does anyone know whether AppleRaid allows a RAID 10?
  2. Boomhowler macrumors 6502

    Feb 23, 2008
    Wouldn't it be more efficient to just raid0 the SSDs and do hourly backups (time machine) of the raid-array to one of the mechanical drives?

    It depends on how critical the information is that you are working with. If you cannot afford to loose even one hour worth of work then you should go with raid10 or something, otherwise I don't see the "point" of not using the ssds in raid0.
  3. percival504 thread starter macrumors regular

    Feb 10, 2009
    Thanks Boomhowler. I agree. That's why I want to go with a RAID 10 (I run a server). I am just trying to confirm that AppleRAID will do a RAID 10.
  4. nanofrog macrumors G4

    May 6, 2008
    If you mean the software capability built into OSX, then Yes. It will do 10.

    It's not as robust in terms of recovery vs. a hardware implementation, but a sufficient backup system should minimize the amount of work that needs to be re-performed in the event of a failure.

    I mention this, as I want to be sure you don't mean the Apple RAID Pro, which is the crappy hardware card. It does 10 as well, but won't offer you any real advantages (slow pile of garbage). Areca or ATTO will, but it's at quite a cost premium.

    As per your drives, 0/1/10 via a software implementation will be fine. But none of them are suited for parity based levels (where typical MLC based SSD's would get trashed due to both data and parity writes ever single write cycle initiated by the application/OS), and the mechanical drives won't work with a hardware card anyway.

    Hope this helps. :)
  5. thekev macrumors 604


    Aug 5, 2010
    You always explain this stuff really well.
  6. percival504 thread starter macrumors regular

    Feb 10, 2009
    Thanks Nanofrog! BTW: I don't understand what you mean by HDDs won't work. I decided to go with the ATTO H608 and Apple's software RAID, but I was planning to RAID some of my HDDs as well. I can always use AppleRAID software, but I am just curious about the inability to use H/W RAID with the HDDs.

    BTW: I was hoping you would show up. :)
  7. nanofrog macrumors G4

    May 6, 2008
    It depends on the card. Specifically, if it's just an interface card (SATA or SAS for example), where the OS has control of recovery, or a RAID card, which takes over that function.

    In the latter case, the card does it differently due to RAID, which means the recovery timings programmed into the HDD's firmware (not a driver) must be designed to work with a hardware RAID card.

    And you can only get these different timings in HDD's designed for RAID (HDD makers do this because they don't want to lose money by users' running consumer grade HDD's rather than buy the RAID variants).

    There are a few other small differences, specifically the addition of sensors not used on the consumer models (same board typically, just more components added + different firmware to utilize them), but the mechanical components are typically the same (some will use cherry picked platters to obtain the higher Unrecoverable Bit Error Rates; motors, heads, enclosure are the same if it's rated for the same RPM/size format).

    Western Digital uses the same platters between the RE versions (RAID Edition) and Caviar Blacks. So in their case, it's just additional sensors on the HDD controller board and different firmware.

    BTW, most consumer drives have an UBE of 10E14, while RAID versions (SATA based on the same mechanics), have a typical UBE of 10E15 (1 order of magnitude improvement). It might not seem like much, but it's important with RAID systems, particularly when parity levels are used (due to the increased write frequency).

    In the case of the H608, it is NOT a RAID card (RAID versions from ATTO begin with an R, so the R608 = RAID version). Just a fast HBA (SATA/SAS interface).

    Any RAID functions will be done via software using the H608 (either OSX or a 3rd party software RAID application if you chose to use one). Personally, OSX's software RAID functionality will do what you want, so there's no need to buy additional software (unless you're after a specific proprietary level not offered by OSX; usually claims improved recovery vs. equivalent level of a traditional software RAID implementation for example).

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