Does fusion work (well) with 3 drives?

Discussion in 'Mac Pro' started by omvs, Aug 4, 2014.

  1. omvs macrumors 6502

    May 15, 2011
    After some upgrades, I have an extra 240G SSD - right now I'm using it for 10.10 testing, but I'm debating a 3 drive fusion - 2x240G SSD & a big hard drive.

    I briefly tried building one, and coreStorage made a volume for me, but I didn't have time to do any testing before ripping it apart. Has anyone tried this and confirmed it still does sensible tiering with more than 2 drives?
  2. hfg macrumors 68040


    Dec 1, 2006
    Cedar Rapids, IA. USA
    I have built a DIY Fusion drive using a pair of SSDs in RAID-0 then coupled with a large hard disk. It worked fine for the duration that I use it. I have since gone to a 1TB RAID-0 SSD array with separate hard disk and no longer use Fusion in my Mac Pro.

    The "man page" for core storage seems to indicate that you can use more drives, but I think it just concatenates them into larger volumes so there is no additional speed advantage as there would be with RAID-0 for your SSDs.
  3. omvs thread starter macrumors 6502

    May 15, 2011
    So I decided to give it a try - rather than make a raid and then fuse the raid, I just fused the three drives directly together.

    It did successfully make a large volume, but the tiered behavior doesnt appear to work - when I write a large file, iostat shows it going to the rotational drive, and no migration occurs when the system is busy.

    I might try the RAID0 + HD, though I'm not very hopeful it will handle that either except as a big drive.

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