RAID0 + TM Backup

Discussion in 'Mac Pro' started by El Awesome, Jul 30, 2012.

  1. El Awesome macrumors 6502

    El Awesome

    Joined:
    Jul 21, 2012
    Location:
    Zurich
    #1
    Hey guys,
    I have three 1TB HDDs in my (newly bought) Mac Pro 4.1. The SSD will arrive tomorrow.
    I wanted to set up a RAID0 with my 3 HDDs, but I heard that this is risky in case that one HDD is damaged.
    Since I set up a TM Backup to an external FW800 drive anyway, do I loose all the data, or can I just throw the damaged HDD out and copy the data from te TM Backup on the other drives and go on with them?

    RAID1 will not be a big advantage I guess - I rather sell the HDDs.

    Thanks for helping! I know that there are many other threads, but I'm a complete newbie to that. I didn't really undestand a thing in the other threads.

    Alex
     
  2. throAU, Jul 30, 2012
    Last edited: Jul 30, 2012

    throAU macrumors 601

    throAU

    Joined:
    Feb 13, 2012
    Location:
    Perth, Western Australia
    #2
    OK i'm not sure what your experience with RAID is, but here we go:

    RAID 0 means that files are spread across all disks on a block basis (as far as the file system knows, it is just a "disk").

    As in, each file may (probably will) have parts stored on all 3 disks. If one disk fails, then all your files on that array are destroyed (the filesystem itself is broken). You will need to restore the entire RAID0 array from backup, once you replace the dead disk and re-create the RAID0 array.

    Sure you'll be able to get the data back from your time machine backup, but you will be down (i.e., not working) whilst doing so. Saving a second or two here and there waiting for disk access may be totally negated by being broken for a half-day while you rebuild your machine and restore from backup (or, it is data you don't care about losing entirely because it can be re-created - like game files, etc).

    It is a trade-off. Do you REALLY need RAID0 speed as a temporary work area? If the answer to that is no, then RAID0 is not really a good idea. However, this is a question only you can answer. Just be aware of the consequences / additional risk.

    IMHO - Only use RAID0 if the space is being used as a temporary high-speed work area (files stored permanently on more reliable storage) or if you do not care about needing to restore from your last backup.

    As far as failure rates go - due to any single failure causing the array to break, your failure rate for the filesystem will be 3 TIMES as likely as a single non-raided drive. Its not just as bad the chance of a single drive failure on a non-raid machine... it is much worse.

    Of course throughput will be roughly 3x a single drive as well, but unless you need the performance, you're just making your machine a lot less reliable.



    I'm not sure if the mac will allow you to do RAID5? If so, you'd be far better off putting the 3 drives in a RAID5 array - you'll give up 1 drive worth of space, but you'll have the capacity to survive a drive failure without needing to go to backup - just replace the dead drive and it will rebuild.

    Given that you'll have the SSD as a high speed work area i am guessing the other spinning drives are going to be more useful to you as bulk storage. RAID 5 is a lot better suited for this.


    If you don't need quite that much disk space, another alternative may be to sell/ditch one of the spinning drives, buy a second SSD and have 2x RAID1 mirrors? THat way you can have an SSD fail OR a spinning disk fail and you are still working.
     
  3. El Awesome thread starter macrumors 6502

    El Awesome

    Joined:
    Jul 21, 2012
    Location:
    Zurich
    #3
    Thank you very much!
    That was the answer I was looking for.

    I guess I don't need the speed, I would prefer a reliable machine.
    RAID5 would mean that I have to get myself a RAID card, which is damn expensive. I guess I'll just sell the HDDs and put the money into a new GPU.

    Alex
     

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