Who knows a good amount about RAID?

Discussion in 'Mac Accessories' started by MattG, Oct 27, 2011.

  1. MattG macrumors 68040

    MattG

    Joined:
    May 27, 2003
    Location:
    Fletcher, NC
    #1
    I'd like to think I do, at least I've been working with RAID devices at a professional level for several years now.

    However at home, I purchased a consumer-grade device for use with my Mac Mini media library. OWC Mercury Pro Qx2. I have the thing setup in a RAID-5 array, using a 3+1 configuration (three drives in the array plus a hot spare). More or less, the safest config you can do on this device and still get a reasonable amount of storage.

    Cut to yesterday morning -- I wake up to the device beeping, to find that one of the array drives failed, as well as my hot-spare. I tried reseating each, one at a time, but...they're bad. My data is still good, but I've now lost the max amount of drives I can lose without replacing a drive immediately. Replacement drives are in the mail and I've backed up my data to another drive just in case.

    My question stems from reading the device manual. It says that when replacing a drive, you need to replace it with the EXACT same make and model, preferably the same firmware revision, etc. I've never known this to be the case with RAID...it's always been my understanding that as long as you replace the drive with one of equal or greater capacity, it will work, and if need be the array will "dumb" the drive down so it only uses the same capacity as all the other drives. Anybody in here have experience doing this? I'd kind of like to order some spares and NOT get the same make/model that I used before, being that two of them up and died on me at the same time.
     
  2. bwhinnen macrumors 6502

    Joined:
    Apr 15, 2010
    Location:
    San Diego
    #2
    Two things come to mind straight away.

    1. RAID5 can only sustain one HDD failure prior to data loss, given that you have two drives failed and still have data available there are alarm bells ringing straight away.

    2. It is the hardware that determines what the drive needs to be replaced with not the RAID standard. So if the hardware you have purchased requires the same make and model as the original then you may be in a little bit of trouble.

    Your best bet is to contact OWC themselves and see what they have to say.

    Brett
     
  3. KScottMyers macrumors regular

    Joined:
    Jul 17, 2009
    Location:
    Orlando, FL
    #3
    He said he lost one Data Drive and a Hot Spare - which is why its running OK at this point - in degraded mode.
     
  4. bwhinnen macrumors 6502

    Joined:
    Apr 15, 2010
    Location:
    San Diego
    #4
    He also said it was configured in 3+1 which is nomenclature for 3 data drives and 1 parity drive in the industry. He only has four slots available in his enclosure, this means that he can only afford to lose one drive in total.

    So unless the OP means he has a 2+1 RAID5 data set and a configured hot spare he is in dire straits :) And if he means that he has it configured that way then point 2 of my original post stands and I'll keep quiet on point 1 :)
     
  5. KScottMyers macrumors regular

    Joined:
    Jul 17, 2009
    Location:
    Orlando, FL
    #5
    Just clarifying - he does say (three drives in the array plus a hot spare).
     
  6. bwhinnen macrumors 6502

    Joined:
    Apr 15, 2010
    Location:
    San Diego
    #6
    I know :) Thus my "keep quiet" comment :) (which I'm obviously not doing right now)...

    I saw 3+1 and my brain went into "work" mode and said that is 3D+1P and completely discounted the hot spare wording... My mistake :(
     
  7. MattG thread starter macrumors 68040

    MattG

    Joined:
    May 27, 2003
    Location:
    Fletcher, NC
    #7
    Thanks -- I did contact OWC and they echoed what the manual says.

    I don't have four drives in the array. I've got three in the array, and one is a hot spare. One of the array drives went bad, and the hot spare went bad, leaving two good drives in the array. All of my data is ok (unless another drive goes bad before I get at least one of the two bad ones replaced).
     
  8. bwhinnen macrumors 6502

    Joined:
    Apr 15, 2010
    Location:
    San Diego
    #8
    That makes migrating to larger drives an issue then in the future (or now if you have 1TB drives and want to go to 2TB or 3TB which the current model seems to support).

    I also assume that given they want the same size, model and firmware that you are 'stuck' into purchasing from them for the replacements and they will be able to supply the replacements? Unless you purchased a bare array of course :)

    Best of luck, do keep us posted and I highly suggest a backup of your data at this point if you don't already have one :)
     
  9. MattG thread starter macrumors 68040

    MattG

    Joined:
    May 27, 2003
    Location:
    Fletcher, NC
    #9
    Oooooh yes, I backed it up :)

    I actually did purchase a bare array from them. You can use whatever drives you want in it, but they just seem to think they all have to be exactly the same...so if I ever want to upgrade my array, I'd need to buy four new drives, back up the old ones, and then replace the entire array at once. :rolleyes:
     

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