An important question before I set up my software RAID

Discussion in 'Mac Pro' started by valdore, Jan 30, 2008.

  1. valdore macrumors 65816


    Jan 9, 2007
    Kansas City, Missouri. USA
    So I was all ready to use Disk Utility to set up a software RAID 0 (striped) until I get a RAID controller. Then, I get the message I'm attaching, saying that if I do this, all the data on the drives will be erased, which surprised me.

    On Drive 1 you would find basically everything since I got this computer last May. Drive 2 is blank, having just gotten and installed it.

    So, does this mean that I have to back up everything on Drive 1 (Time Machine), then erase the whole drive, and then reinstall everything?

    I'm lost and I need help. Thanks.

    Attached Files:

    • raid.jpg
      File size:
      123.7 KB
  2. hfg macrumors 68040


    Dec 1, 2006
    Cedar Rapids, IA. USA
    Yes ... for RAID 0

    If you really want RAID 0, where your two drives work in parallel (both transferring data at the same time for more speed and double the storage capacity), then yes, you have to start from scratch and reload the RAID array with your OS image. The data is equally distributed over both drives at once.

    If you just want to concatenate (JBOD) the two drives to make a larger "logical" drive, but not transfer the data in parallel, then you shouldn't have to reload the boot disk you have.

    If you want RAID 1, where one disk is continuously mirrored to another (no increase in speed, no increase in total capacity, full redundancy), I believe it will build the second drive from the first without having to reload it.

    If you have 2 500GB drives:
    JBOD: 1000GB Capacity no speed increase, no data redundancy
    RAID0: 1000GB Capacity double transfer rate, no data redundancy
    RAID1: 500GB Capacity no speed increase, full data redundancy

    Note that if a single disk fails, you could lose up to half your data (depending on which disk failed) with JBOD, you will lose everything with RAID0, and your data should be safe on the other disk with RAID1.

    Hope that helps...
  3. valdore thread starter macrumors 65816


    Jan 9, 2007
    Kansas City, Missouri. USA
    Thanks, Howard.

    It sounds like the most logical thing for me would be the JBOB/Concatenated, as I'm not too concerned about data writing speed. And, this darn time machine backup looks like it's going to take about 24 hours to transfer to the external.

    Thanks for the information.
  4. phjo macrumors regular

    Jan 8, 2008
    One more thing...

    You can configure a raid array with volumes instead of physical harddrives... I did just that to have a fast raid 0 array of 150Gb (first partition of 75Gb of two harddrives) and the rest could be set as a mirrored raid 1 or no raid at all.

    But yes, if you intend to use raid on your boot harddrive, you'll have to reinstall (or, probably faster, clone it)

    phjo (who prefer to use CCC for that than time machine... not sure he'll ever use time machine anyway...)
  5. valdore thread starter macrumors 65816


    Jan 9, 2007
    Kansas City, Missouri. USA
    Looks like I'm getting the warning that all data will be wiped even for Concatenated JBOD and also Mirrored RAID 1. :confused: This sucks.
  6. johny5 macrumors 6502a


    Mar 31, 2007
    Forgive me if I am wrong but RAID 1 should also offer some speed increase if the Mac Pro supports multithreaded split seeks, does anyone know if it does?

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