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Raid 3

Discussion in 'Macintosh Computers' started by crashtd, Nov 3, 2003.

  1. macrumors newbie

    i'm thinking of setting up a RAID 3 HD setup. Wanted to pick your guys' brains first though...

    Controller cards? Which one to get? What is the average perfomance increase over just s/w controlled RAID?

    I'm figuring to use ATA drives, and recommendations? I was thinking 2x120GB and 1x240GB??

    thanks for the advice in advance folks

  2. macrumors 6502

    Look on the web for what RAID you want to set up:

    For example:
    Speed (RAID-0)
    Security (RAID-1)
    Both (RAID-5, RAID-10, RAID-0+1)
    JBOD (your mileage may vary)

    Typically a RAID system (striped or mirrored) is symetrical, so you could use your 120MB in a speed (RAID-0) or security (RAID-1) configuration. Using the 240 with the 120s puts you in the JBOD category.

    If you want to use hardware RAID in the "Both" category, prepare to shell out the big bucks, and it is most likely SCSI. The "advanced" IDE RAID solutions are somewhat laughable, next to their SCSI cousins.

  3. macrumors newbie

    Well what are the rough figures in difference on performance?

    I wanted to stripe the two 120's and Mirror them with the 240, sound right?

  4. macrumors 68020


    Sounds as though you need to do some basic reading on RAID. How does striping two drives and mirroring them make it RAID 3? It doesn't. You are talking about RAID 1+0 (or 0+1). Unless you are using the term "mirror" when you are really talking about a "parity" drive. All the drives need to be the same geometry and speed; you can't mirror a two-drive stripe onto a single drive (and even if you could, you would lose performance, since the single big drive becomes a bottleneck).

    In any case, there's plenty of good info about RAID out on the Web. You really have to decide what your goals are in terms of performance, reliability and cost before you can determine which RAID configuration is the optimum for you.
  5. macrumors regular

    We have a Medea RTR setup (IDEs on a scsi bus) at our production. It is possibly the worst drive setup ever. It is incredibly unstable and has constant failures. And it is not cheap.

    Stay away from these drives!
  6. macrumors newbie

    so can i get a clueless point?? :p

    how is a 1+0 different from just a striped drive setup, and a third drive that just a retrospect or equiv backup, there's some performance/redundancy benefit right?

  7. macrumors 6502

    0+1 needs 4 drives last I checked. All should be about the same geometry, but most RAID cards can use the lowest common denominator when defining an array.

    You could use your 3 drives in a RAID 5 configuration...

    That would mean you would have 240MB total ((n-1)*capacity), (the 240GB drive would only be 50% utilized since the drives have to be symetrical) but it would be striped and "xor'd" so any one loss of a drive wouldn't lose data.

    The only thing is you need a card that can do RAID 5 IDE on a Mac (I use a Promise FastTrack SX4000, but it is on a PC running Linux- and there are no Mac drivers). Since a RAID 5 has to read/write to all drives concurrently, typically speed is boosted over a single drive, but still less than 0 or 0+1 configurations. I've found that the speed boost is actually quite minimal (the Promise card does most of the RAID work on the CPU anyways), and I have to hope it survives if a drive dies. I'd say my cheap RAID 5 experiment is pretty much that - cheap, and you get what you pay for in this case.

  8. macrumors 6502

    Some basic definitions and application suggestions for RAID setups.

    Here's one...

    ...and another.

    Those are a couple of places to start looking at to determine which type of RAID will best suit your purposes. One thing, tho. Get a hardware RAID controller. Software doesn't cut it from a reliability standpoint.

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