Mac Pro Raid Setup Help

Discussion in 'Mac Pro' started by Vz909, Feb 28, 2010.

  1. Vz909 macrumors newbie

    Joined:
    Feb 28, 2010
    #1
    Hi I need some help seting up raid 0 for my mac pro 3,1. Right now I have the stock 320GB drive that I use with Mac OS X, and an additional 500GB drive running Win XP through Bootcamp.

    I read on apple's site that you could stripe multiple drives to create a raid 0 to increase performance on the Mac Pro w/o the raid controller card. So my question is how do I do that? I'm in the process of picking a new 2TB drive to set up the raid with the 320GB OS drive. Since the 500GB one is dedicated for XP I don't think I could include it in the raid right? Sorry I'm a tech newbie and help is appreciated. :)
     
  2. NoManIsland macrumors regular

    Joined:
    Feb 17, 2010
    #2
    The drives used in a RAID need to be the same size. If you got another 320 GB drive, you could use the OSX Disk Utility to set up a software RAID 0.
     
  3. vvrinne macrumors member

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    Feb 28, 2010
    Location:
    Helsinki, Finland
    #3
    I don't think the drives need to be the same size (atleast for software raid)? Won't the raid size just be determined by the smaller drive?

    OP: You should be aware that with a stripe (RAID 0) setup you will loose all your data if one of the disks in the stripe fails. You could consider setting up a striped mirror (RAID 0 + 1) or mirrored stripe (RAID 1 + 0). With these kinds of configurations you get the performance benefits of the striped without loosing your data. You need 4 disks for these though, which is not an option for a lot of people :)

    If you are just looking for a performance boost I would personally recommend against the raid setup and just go with an SSD like the Intel X-25, which will blow any raid setups out of the water. Just my 2c though.
     
  4. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #4
    Actually, that's not the case at all.

    They don't have to be the same size, make or model. Capacity would be based off of the smallest drive in the set, and the slowest drive would dictate the speed as well. Think slowest and/or smallest link in the chain (drives can't hold capacity they're not rated for, nor can they run faster than they're designed). The speed and capacity increases is due to parallelism of the drives in the set.

    This applies to either software or hardware implementations BTW.
     
  5. NoManIsland macrumors regular

    Joined:
    Feb 17, 2010
    #5
    Fair enough, but at the very least it is good to point out that a RAID between a 320 GB HDD and a 2 TB HDD is inefficient to say the least.
     
  6. Vz909 thread starter macrumors newbie

    Joined:
    Feb 28, 2010
    #6
    Okay so based on the replies so far, it'll be better if I get 2 of these 2TB drives and stripe those two together in a raid 0/1 setup (or a raid 0) am I correct? And I could do that in the Disk Utility software setup?

    To be more specific I will need the raid setup because I just started HD video editing and the raid drives will be the media drives where the video is stored and accessed, so I need both reliability and speed in my setup.
     
  7. vvrinne macrumors member

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    Feb 28, 2010
    Location:
    Helsinki, Finland
    #7
    Well if you need both reliability and speed then you need a striped mirror or a mirrored stripe.

    The stripe part (raid0) is the process of combining two disks to create a larger logical disk so 1+1 = 2. This increases performance because data is spread on two disks instead of one and there is more bandwith available for reading and writing. It's a case of diminishing returns though so it's not a 100% increase in performance. If either disk fails all data on the whole array is lost. So from a reliability perspective this is a bad solution (twice the risk of loosing all data).

    To add reliability you can mirror your stripe. You create a second stripe of the same size and set it to mirror the original stripe and you can have a single disk fail on either stripe and you are still good to go. You can even have two disks fail as long as they are in the same stripe. If two disks fail on opposing stripes all data is lost.

    Then there is the concept of striping a mirror. This is basically the previous scenario in reverse so you need to set up two mirrored disk and then you stripe those. The difference lies in what happens when a disk fails. As far as I am aware the 1+0 configuration (striped mirror) is superior in that a single disk failing will not cease operation. In the 0+1 configuration (mirrored stripe) a disk failure will make the whole volume invalid until the disk is restored. No data is lost in either case.

    So to make a long story short. If you want performance and reliability and can afford it then buy 4 identical disks and set up a striped mirror (1+0 configuration). This will give you the performance benefits of a stripe while still withstanding the loss of a drive (or two if you are lucky). If you are doing this with software raid you just need to plug in the 4 disks, then create two separate mirrors (2 disks each) and then create a stripe of the two logical volumes that are your mirrors. Then you end up with a single logical volume that has the space of 2 of your drives.
     
  8. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #8
    I figured with the information I gave, the capacity difference would be common sense. :eek: :p

    Ultimately, the capacity difference is unusable unless it's set aside via a partition, and simultaneous access will degrade the throughput of the array. :rolleyes: There's always a cost with RAID, especially for situations like this... ;)

    But yes, the point you've mentioned is important. In the instances it's done anyway, it's due to lack of budget, or it's created out of what ever's on hand (no desire to spend money, even if available).

    A stripe set (RAID0) has no redundancy at all. That means, if the any drive fails, your data is gone. Period. Recovery must be done from backups (no other possibility - if you don't have a backup, you're toast).

    You need redundancy, and the only level software RAID can provide (OS X's Disk Utility), is 0 + 1 or 1 + 0 (aka 10, and is safer than 0+1). But it requires 4x disks to make it work.

    If you need more capacity for that set of drives, you'll have to get a RAID card (proper unit, not Fake RAID) that can do a level 5 properly (has an NVRAM solution to the write hole issue associated with parity RAID). I'd recommend Areca for a manufacturer. Example card (note that it has it's own processor and cache, and it can even boot EFI = OS X).

    I'd recommend reading up on the RAID wiki page, as there's a lot of good information there.

    Also, let me make this as clear as I can: RAID is NOT a backup. You need backup when using drives of any kind, whether run as a single disk, or RAID. You can use a RAID to backup another RAID, but they're separate arrays, and the data transfers are handled via backup software, not the card (it's firmware and/or drivers).

    Hope this helps. :)
     
  9. hoya87eagle91 macrumors member

    Joined:
    Apr 29, 2005
    #9
    so based on the above, with the three empty drives in a Mac Pro, could you configure two drives in raid 0 for speed and use the third drive for a time machine drive to back that up that raid 0? All just using disk utility? Will this speed up up HD video editing for iMovie and FCE? How would it help Photoshop if at all? Thanks
     
  10. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #10
    Yes to every single question. :)
     
  11. tomllama macrumors regular

    Joined:
    Jan 7, 2007
    Location:
    CA
    #11
    The original poster mentions boot camp ...

    You can't access an OSX software RAID when you run boot camp, the disks will simply sit idle. If you have the software RAID disks connected via eSATA in an external case, you will not be able to see them from boot camp either unless the eSATA card you use has both OSX and Windows drivers.

    If you want to be able to use a software RAID with Windows and OSX both, then you will likely need to run Windows in a virtual machine (like Parallels).

    A 'real' RAID (hardware, not software) that is fully functional for both OSX and Windows is not cheap.

    Also note that a time machine that is smaller than the information to back up is not going to be able to hold much. If you have a 4 TB RAID, a 2 TB time machine will be worthless once your RAID is 50% full (and the time machine will be marginal after it's 20% full).
     

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