Should I RAID the "cache" drive or the system drive?

Discussion in 'Mac Pro' started by DaSal, Mar 3, 2009.

  1. DaSal macrumors regular

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    #1
    I have 3 drives in my system, one 1,5tb one and 2 1tb F1 drives. I've been thinking about making a mirrored raid out of the 1TB f1's. I was wondering though, would I see the greatest performance increase by using the raid as my system drive (the OS, apps, etc), or the drive where I keep my Final Cut scratch, etc?
     
  2. belvdr macrumors 601

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    #2
    For mirroring, you usually notice the big improvements where a lot of reads are taking place. Writes can be slower for a mirror.
     
  3. DaSal thread starter macrumors regular

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    #3
    Ok... So... If I'm doing it for video editing (Final Cut, After Effects), I'd get the best performance by storing my video on the mirrors, as the applications read it from the drive?
     
  4. belvdr macrumors 601

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    #4
    Potentially, but only if you are reading a bunch of data. If you are also writing a bunch of data, it may take just as long. When the discussion turns to high-performance RAID arrays, you really should look at hardware controllers that support RAID 10/01. Software mirrors really only assist in recovering from hardware failures. They do little for performance (in fact may reduce performance).
     
  5. DaSal thread starter macrumors regular

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    #5
    I see. So considdering I would be using a software raid it's probably better to just not use a RAID at all, and backup manually when needed?
     
  6. belvdr macrumors 601

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    #6
    That's what I'd do. You can always try the mirror and if it doesn't work, break it and use the extra drive for something else.
     
  7. yippy macrumors 68020

    yippy

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    #7
    Whoa whoa whoa.

    Mirroring does not increase performance, it only protects against drive failure. In fact, unless you have a very good RAID card, mirroring will cause a slight decrease in performance.

    Now stripping (RAID 0) will increase performance and it would probably be best to do this on your scratch/working drive. But make sure you BACK UP your data as RAID 0 doubles the chance of loosing your data to drive failure.
     
  8. belvdr macrumors 601

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    #8
    No, mirroring can also help in read performance. I'm not sure how OS X does it, but if you are reading data from a mirrored array, the controller can use both drives to read that data. This is especially helpful where multiple files are being read at once.

    I'm not sure how it could decrease read performance in any way. There's no parity calculated on RAID 1, and even if you don't use the second drive, you are still reading from the first.
     
  9. yippy macrumors 68020

    yippy

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    #9
    Read I could buy, but write performance does take a hit.
     
  10. belvdr macrumors 601

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    #10
    Agreed, hence my first statement. :)
     
  11. xraydoc macrumors demi-god

    xraydoc

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    #11
    And don't forget - a mirrored RAID is NOT a backup. It helps protect from hardware failure, but its not a backup - delete something by accident or get a corrupted file, its gone from BOTH drives.
     
  12. DaSal thread starter macrumors regular

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    #12
    Right... I see. I'm confused, what do people usually do? Make a RAID 0 and then mirror that? (4 hd's?) Is that possible? Not that it's applicable to me anyway, just curious. I assume one can't raid partitions on different drives? In that case I could make a 1tb raid with 2x500gb partitions and then a 1tb mirror with the other 2x500gb partitions. I don't think this is possible though, is it?
     

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