RAID-0 with different drive capacity

Discussion in 'Mac Pro' started by Jardins de Vin, Feb 2, 2017.

  1. Jardins de Vin macrumors 6502a

    Jardins de Vin

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    #1
    I've heard that if you have two drives with different capacity, you will be limited to the slower one when making a RAID-0 configuration. The drives that I would combine however, seem to have the same read & write specs.

    It's a Samsung 850 Pro SSD. The one I have is 512 GB and the one I would buy would be 1 TB.

    According to this site… http://www.anandtech.com/show/8216/samsung-ssd-850-pro-128gb-256gb-1tb-review-enter-the-3d-era

    … they both have the same read & write specs. What do you think? Is it okay to create a RAID-0 config with them?
     
  2. beaker7 macrumors 6502a

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    #2
    You can but you'll be capacity limited to 1 TB total.
     
  3. flyinmac macrumors 68030

    flyinmac

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    #3
    What is your goal?

    Taking 1.5 Terrabytes of SSD and turning it into 500 GB doesn't seem to accomplish much.

    Personally, with an SSD, I wouldn't bother with RAID 0. SSD drives are already pretty fast.
     
  4. usna92 macrumors member

    usna92

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    #4
    Agreed. Though in Sierra you do have the option of creating a JBOD which would allow you to access all the capacity of the drives but access it as one logical volume.
     
  5. Jardins de Vin thread starter macrumors 6502a

    Jardins de Vin

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    #5
    Yes, I would like to have more space (and have them all in one volume) and more speed. I could get twice the speed I have now if I would be using RAID-0.

    Some people also recommended me JBOD. Does it also work in El Capitan? I don't like updating.
     
  6. beaker7 macrumors 6502a

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    #6
    Raid0 would yield 1TB. 512 from the 512, and the other 512 from the 1TB.
     
  7. usna92 macrumors member

    usna92

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    #7
    Which essentially wastes 512 on the 1TB. I don't know if the JBOD option is in El Cap or not. I have to run release and betas for work, so haven't done a lot of looking back into disk array options in the older OS. If you're on the internal SATA. I do not think you are going to see an increase in performance from your SSDs in a Raid-0 configuration. I think you would be better off using them individually or if you really need the performance of a striped SSD, I would buy another 512 and then stripe them on a raid controller.
     
  8. MacUser2525 macrumors 68000

    MacUser2525

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    #8
    No it does not you end up with that as a usable partition on the 1t drive it will not be raided just a normal partition. If doing the raid creation on El Capitan you will need to look at the instructions for doing it via the command line as Apple removed that functionality from the GUI of Disk Utility.
     
  9. AidenShaw macrumors P6

    AidenShaw

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    #9
    You're describing a "concatenated volume" or a "spanned volume".

    JBOD is "just a bunch of disks" where each disk is a separate, independent volume. In others, one 512GB disk and one 1TB disk.

    Many software volume managers (Windows, Linux,...) would allow you to make a 1 TB RAID-0 volume across the two drives, and create a second 500TB volume from the remaining space on the 1TB SSD. Nothing would be wasted.
     
  10. kschendel macrumors 6502a

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    #10
    Raid0 (striping) gets its speed by splitting files across the N drives involved. In situations where you can issue N reads or writes more or less simultaneously, you can get up to an N times improvement in speed. Of course, you don't normally get this much because controllers or busses get maxed out.

    This only works if you can divide things up evenly, which is why a raid0 on your proposed SSD's will only use the size of the smallest (not slowest) from each drive. In your case, 512 Gb each, totalling 1 Tb, and the remaining 512 Gb on the 1 Tb drive can't participate. As others have said, given the right partitioning, you can use that space as a separate drive, but it won't be part of the striped volume.

    I do think that the SATA controller can handle more throughput overall than a single SATA-II link, so you might in fact see some benefit from striping. I don't know that that's the most effective way to more speed, though; a single PCIe drive ought to be able to beat a SATA striped volume quite handily.
     
  11. flyinmac macrumors 68030

    flyinmac

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    #11
    Yes, you're correct. I was thinking of the mirrored setup.

    In reading the later posts, it does sound like the OP's goal would be better met by a volume spanned over two drives.

    Already being an SSD, the performance of RAID seems less important.

    The only advantage might come from each drive independently delivering bits of data simultaneously. But with SSD, it's going to be less noticeable.

    As for spanning a volume, much like a fusion drive, the potential downfall is that if you have one drive fail, then you end up losing all data from both drives (including the data from the drive that didn't fail).

    That brings out the real power of other RAID configurations (parity, mirrors, etc.), though additional drives are required and not all of them extend your capacity. If I was going to go into RAID, it would be for redundancy and data protection.

    Personally, unless it involves mirrors and / or parity, I'm not a fan of spreading my volumes across more than one drive. But obviously, that is up to the OP to weigh the risks and benefits based on his / her preferences.
     
  12. Acden macrumors member

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    Aug 13, 2016
    #12
    There is no problem to get disk utility from the older versions for accessing of creating RAID volumes!

    So, divide 1TB into 2 volumes. Then in disc utility make one of them stripped with other physical SSD. And you will get 1TB RAID + about 480GB other volume.
     
  13. flyinmac macrumors 68030

    flyinmac

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    #13
    Makes sense.

    But the OP is wanting everything to appear as one volume. So in this scenario, he'd still have 2 volumes.

    While I personally wouldn't go down this path, that is up to him / her.

    But, if I was inclined to go the route that the OP is seeking, and I wasn't concerned about the idea of one drive failure killing data on both drives, then I think the following is what I'd pursue.

    OP has a 512 GB drive and a 1 TB drive.

    To avoid wasting space, while still obtaining a single volume using RAID 0 for performance purposes, I'd purchase a second 512 GB drive. And then here comes the fun part.

    Take the old 512 GB drive, and the new 512 GB drive, and join / combine them into a single 1 TB spanned volume.

    Now, take the resulting 1 TB spanned volume, and the other 1 TB SSD drive, and create your 2 TB RAID 0.

    As to whether the above scenario is easy on OS X, I don't know. I do know that it's simple in the enterprise industry with servers running Linux and Windows 2012 R2. I've configured the above numerous times on enterprise servers (which I then pulled into other Arrays for redundancy).

    Never tried it in OS X.

    Naturally, I prefer an arrangement with mirrors and / or parity. That's the biggest reason to use RAID in the enterprise market. Hot swapping a failed drive without any data loss (while benefiting from increased speed).

    If you want to go nuts, take two or more RAID Arrays, and then combine those Arrays into another RAID.

    You can get the performance up there. And have multiple levels of redundancy protecting your data.

    In the home arena, I'm happy with the simplicity of one volume per drive, and backup copies of important data.

    But, if I had the money to throw around, I'd probably go nuts at home too. But for me to get interested, I'd probably go RAID 5 at minimum. And likely either RAID 6 or RAID 10. Naturally, a lot of money. Hence why I settle for my current home set up.
     
  14. orph macrumors 6502a

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    #14
    id gess if your going to do this a PCI card that lets you mount 2 ssd's might be the best option if your going to do this.
    might be simpler to buy a second 500GB card or two 1TB cards but will be fun to hear how it go's
     
  15. hfg macrumors 68040

    hfg

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    #15
    I have done this in the past (on purpose) with 2 different sized drives. I wanted both OS X and Windows available for boot, and wanted maximum performance on OS X. I split a 1TB drive into two 512GB partitions and created a RAID-0 for OS X using one of the 512GB partitions, and another separate 512GB disk. I then installed Windows on the remaining partition of the larger drive.

    I don't recall having any problems with that arrangement for as long as I had that setup in use.
     
  16. Jardins de Vin thread starter macrumors 6502a

    Jardins de Vin

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    #16
    I don't worry about losing data, I have other external drives which I use for backing up (which should be no different in a RAID-0 configuration I believe?)

    Actually, I only have a 512 GB SSD at the moment. The reason I mention the 1 TB SSD is because I found a new, really cheap one, for half the new price. It's exactly the same SSD as mine but in the 1 TB version.

    What if instead I get another 512 GB one, and I do a RAID-0 config? Do you believe I will also win in speed? I would like to keep them in the optical bay. I read that even if they're in the optical bay, if I have a RAID-0 configuration, it should be twice as fast. Connecting them with PCIe would be a solution too, but apparently having a RAID-0 config with the drives in the optical bay would already reach the drives' maximum read & write speeds, so it would be useless to connect them with PCIe.
     
  17. flyinmac macrumors 68030

    flyinmac

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    #17
    Sounds like a good plan with two drives matching in size.

    As for speed, it's really hard to say if the benefit will be something you'll "feel" or notice (compared to not using RAID with SSD). But it will likely be faster in benchmarks / performance tests.

    There's always potential for there to be a line between what you can feel / notice. It may be significantly faster, but will it reduce the amount of time that your waiting by an amount that you can feel while using the machine.

    For example, I might not feel the difference between 0.25 and 0.5 seconds.

    So if without RAID I get a file open in 0.5 seconds. And with RAID it opens in 0.25 seconds. Then it may not be noticeable enough to justify the process/expense.
     
  18. Jardins de Vin thread starter macrumors 6502a

    Jardins de Vin

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    #18
    I wouldn't feel that difference either. From what I've read, Read & Write speeds should be twice as fast (going from around 250 MB/s to 500 apparently). Since I have to load big plugin libraries all the time (music production) I was hoping that it would become faster :)

    I am running out of space anyway, so I will most likely get another 512 GB. I won't cost me anything to try out a RAID configuration. But do I have to make a fresh install of OS X?
     
  19. flyinmac macrumors 68030

    flyinmac

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    #19
    You don't need a fresh install of OS X.

    But if you want to avoid doing a fresh install, you will need to clone your existing installation to another bootable drive first.

    Then set up your RAID and then clone your installation back to the new RAID.

    Make sure you clone your recovery partition as well.

    Cabin Copy Cloner is the best program in my experience. But there are naturally those who prefer different programs to clone installations.
     
  20. flyinmac macrumors 68030

    flyinmac

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    #20
    Darn auto correct. Carbon Copy Cloner. Not Cabin. Lol.
     
  21. MacUser2525 macrumors 68000

    MacUser2525

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    #21
    No recovery partition is possible on RAID boot drives your only choice is a spare non-raid drive for that to be done and usable.

    Code:
    MacUser2525:~$ diskutil list
    /dev/disk0 (internal, physical):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      GUID_partition_scheme                        *480.1 GB   disk0
       1:                        EFI EFI                     209.7 MB   disk0s1
       2:                 Apple_RAID                         30.0 GB    disk0s2
       3:                 Apple_Boot Boot OS X               134.2 MB   disk0s3
       4:                 Apple_RAID                         449.6 GB   disk0s4
       5:                 Apple_Boot Boot OS X               134.2 MB   disk0s5
    /dev/disk1 (internal, physical):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      GUID_partition_scheme                        *120.0 GB   disk1
       1:                        EFI EFI                     209.7 MB   disk1s1
       2:                  Apple_HFS EL_SSD                  39.3 GB    disk1s2
       3:                 Apple_Boot Recovery HD             650.0 MB   disk1s3
       4:                  Apple_HFS iMac_TM                 79.6 GB    disk1s4
    /dev/disk2 (internal, physical):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:      GUID_partition_scheme                        *480.1 GB   disk2
       1:                        EFI EFI                     209.7 MB   disk2s1
       2:                 Apple_RAID                         30.0 GB    disk2s2
       3:                 Apple_Boot Boot OS X               134.2 MB   disk2s3
       4:                 Apple_RAID                         449.6 GB   disk2s4
       5:                 Apple_Boot Boot OS X               134.2 MB   disk2s5
    /dev/disk3 (internal, virtual):
       #:                       TYPE NAME                    SIZE       IDENTIFIER
       0:                  Apple_HFS EL_RAID                +60.0 GB    disk3
    
     
  22. orph macrumors 6502a

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    #22
    well if you can get a 1TB cheep might be worth it, one thing is that a single SSD will get close to that speed in a PCI card i think.
     
  23. Acden macrumors member

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    Aug 13, 2016
    #23
    Why not to use standard Disc Utility to clone?

    And why do you need to clone recovery partition? (I think when you recover your desktop, it is best to install the newest OS version from USB drive, not to see this partition every time).

    I wil try to insisnt on 1TB, again. Look, you could make RAID 0 with a half of this partition. And the rest (which is free for you by money!) 500GB is for other data logical drive.

    If you have a chance to buy new 1TB, why to buy 500GB? Is it enough for you? As for me, I have a lot of 500GB/1TB USB drives for data. But I don't want to buy SSD for data as the don't live long, as I understand (my hdd's most of them are 10-years old, for example, my Sony laptop HDD is from 2008 year).

    By the way, with 500+500 you will get 1TB for system drive! It is enough. But why not to have additional SSD 512 GB free space for no cost?
     
  24. flyinmac macrumors 68030

    flyinmac

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    #24
    Disk utility isn't ideally suited for the task of making a bootable clone.

    The recovery partition is useful for disabling certain OS X settings that sometimes get in the way of tweaks that we might need to make.

    It is also useful for trouble shooting some problems.

    It isn't just used for reinstallation
     
  25. Acden macrumors member

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    Aug 13, 2016
    #25
    1 I did with no problems...

    2 What settings for example?
    You can use temporary boot usbfor these reasons instead of having spare volumes un the finder or other soft lists.
     

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