Raid Idea's

Discussion in 'Mac Pro' started by Etherz10, Oct 2, 2010.

  1. Etherz10 macrumors member

    Aug 27, 2008
    United Kingdom
    I currently have 2 x 250GB drives in raid 0 (software raid) is it possible to have

    1 x 250GB + 1 x 750GB in 1TB Raid 0
    1 x 1TB Drive Raid 1 of the Raid 0
    and sell off the other 250GB drive

    Help Please

    Thanks in Advance
  2. Transporteur macrumors 68030

    Nov 30, 2008
    No. RAID 0 requires (at least) two similar sized drives or partitions.

    Don't understand that.
  3. Honumaui macrumors 6502a

    Apr 18, 2008
    no :) (Transporteur beat me to it)

    you could do the 250 and 750 in JBOD

    I would ask what are you trying to do ?
    more storage ?
    faster ?
    safer ?

    maybe list the make and model of the HDD and you can get more configuration thoughts ;)
  4. Etherz10 thread starter macrumors member

    Aug 27, 2008
    United Kingdom
    i wanted to have a 1tb raid 0 (250+750) with the 2 drives and then have the other real 1TB drive to mirror the 250+750 raid 0
  5. waloshin macrumors 68040

    Oct 9, 2008
    To actually answer your question properly which hasn't been answered right yet, I have used raid many times.

    You want to run raid 0 so if your using a 250 gb and a 750 gb harddrive in raid 0 all your going to have is 250 gb's of storage.

    250 gb will be it nothing more.

    If you use two different sizes of harddrives the smaller harddrive will be dominate.

    Also if you want a raid 0 (stripping) with raid 1 (mirroring) you will need to run raid 10 which will need four harddrives. And still only have a usable space of 250 gb.

    Just run the raid 0 if you want performance, with the two 250 gigabyte harddrives then use the 1 terabyte drive to back it up.

    Also software raid is pretty much pointless.

    Also if you raid 0 the 750 and the 250 you will only have 250 gb's of storage space.

    You will need to run jbod to have 1 terabyte with the 750 and 250 which I believe was mentioned earlier.

    Unless you are doing some data sensitive video work or something just do normal backups daily and you'll be fine modern day harddrives are quite reliable if you buy good brands such as Seagate or Western Digital.
  6. Transporteur macrumors 68030

    Nov 30, 2008
    You get 500GB of storage with a RAID0 out of a 250GB and 750GB drive.
    The smallest drive in the array specifies the array size, which is twice the size of the drive. The other 500GB of the 750GB drive will be wasted.

    The option to create a RAID 0 of these drives and not lose any space is to partition the 750GB into a 250GB and 500GB partition and create an array of the first partition and the 250GB drive. I wouldn't recommend this, though.
    You're better with a simple JBOD as Honumai stated.

    Again, the array size will be 500GB, not 250GB. And just FYI the correct level for this would be 0+1, not 10. ;)

    I wouldn't deal with RAID and different hard drive sizes at all, especially not if the second array member is three times as large as the first member. That's just too much wasted space.

    What makes you think that?

    500GB. :p


    Good point.
    The OP's hard drive requirements aren't really suited to apply a decent RAID, which is why I wouldn't touch it. As mentioned earlier, create a JBOD from the two smaller drives and back it up to the 1TB drive with TimeMachine, CCC, SuperDuper or whatever you like.
  7. Honumaui macrumors 6502a

    Apr 18, 2008
    I am going to ask this again of the OP :)

    I would ask what are you trying to do ?
    more storage ?
    faster ?
    safer ?
    list the HDD you have now :)
    what do you do for BU now ?
    I would also ask do you have a budget to expand or get a few things if needed to accomplish your goal ?

    you cant do what you want :) but if you say OH I want faster storage as I want to get into tinkering with video a bit ? then other video people can jump in and help etc..
  8. smosse macrumors newbie

    Sep 26, 2010
    Transporteur is right

    what you can do
    0+1 2 disk stripped mirrored on 2 other disk stripped
    or 1+0 2 disk mirrored stripped with 2 disks mirrored :)

    or Raid 50 ....... :)

    But i also agree, and that's what i do .. do a Raid 0 of 2 disk of the same size for perf and just backup, backup ,backup :) yes i use 3 backup :D
  9. nanofrog macrumors G4

    May 6, 2008
    If you build a stripe set out of mismatched capacities, the overall capacity will be based on the smallest disk. That is, if you've a 250GB + a larger drive, 750GB in this case, you'd only get 500GB of usable capacity. The remaining 500GB would be inaccessible, unless you partition the 750 into a 250 and 500GB partitions.

    Even if you do this, there's a couple of issues to be aware of.
    1. You can have performance issues if you try to access both partitions on the 750GB disk at the same time (simultaneous access).
    2. There's also additional wear and tear on the 750GB, as it will be accessed more often than the 250GB disk that comprises the stripe set with the 250GB partition.

    Hence the reason to stick with same capacity disks, and if possible, the same models.

    OK, that's the end of the "Quick and Dirty" with the drives you're trying to do with what you have. ;)

    If you'd like more information on RAID in general, I'd recommend giving the RAID Wiki a thorough read.

    BTW, the MP is capable of 0/1/10 only (10 is safer than 01, and IIRC, Disk Utility only allows 10 for that reason).

    As per your situation, I'm with Honumaui here; what are you trying to do and why? And what is your backup scheme (you need one, whether RAID is used or not, but especially with striped sets)?

    Please understand, the information you provide can help steer you in the right direction. :)

    500GB, not 250GB. But the total capacity is based on the 250GB disk (always the smallest member; same goes for other levels).

    Technically, what you've described is a 1+0 or 10, not 0+1 or 01. The order you proceed makes the difference. So if you start with a stripe set, it's 0+1. 10 starts with creating both mirrors first, then striping the pair of mirrors together.

    And assuming the capacity is based on 250GB as the smallest drive, the overal capacity would still be 500GB, not 250GB.

    Not necessarily. It can allow users to save money on levels that have little overhead to operate, such as stripe sets. 1 and 10 are also light on resource requirements, and are acceptable for software implementations for many as well.

    It all depends on the specifics, but cost usually trumps everything else for most users. And unfortunately, software RAID has a significant advantage over hardware RAID implementations in that regard (not just the cost of the card, but you need to use enterprise disks with a proper hardware RAID card, and they're more expensive per disk as well, so it's worse than many would expect).

    Sadly, the majority of drive makers are sporting ~10 - 13% defect rates lately for their consumer drives. :( Which is worse than past figures, in case you're wondering.

    That said, they're not all that bad yet, and consumer disks are cheap enough to be considered disposable. Seriously, when compared to the value of the data stored on them (even personal use IMO, as family photos and movies are priceless to many).

    Not unless the OP springs for a hardware RAID card, and sufficient enterprise disks to go with it. :eek:

    Besides, you don't want to run parity or nested parity arrays in a software implementation, due to the fact it can't deal with the write hole issue.

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