Will a partitioned Fusion drive still swap files?

Discussion in 'iMac' started by hardtofin, Oct 31, 2013.

  1. hardtofin macrumors newbie

    Joined:
    Mar 4, 2009
    #1
    Hi guys,

    As per the title. If I partition my Fusion drive (I usually have an OSX partition and then a Home partition where I store all my data) will the "Fusion" aspect of the tech still work correctly? For example, if I was to have a game on my "Home" partition and used it frequently, would my mac still move it across to the SSD portion of the drive?

    I have googled around but can't find an answer to such a question.


    Many thanks guys!

    hardtofin :)
     
  2. mikochu macrumors member

    Joined:
    Jul 24, 2011
    #2
    Fusion Drive with partitions don't work out well, from what I understand...
     
  3. hardtofin thread starter macrumors newbie

    Joined:
    Mar 4, 2009
    #3
    That means it doesnt work at all, or what exactly? :D
     
  4. Bear macrumors G3

    Joined:
    Jul 23, 2002
    Location:
    Sol III - Terra
    #4
    I don't know that it would work. And I see a technical reason where it might not work and I see a bunch of negatives.

    Would you partition both the SSD and HD portions of the Fusion Drive to make 2 fusion drives (if it is even possible to do that)? How would you decide how much of the SSD to give each partition. You're best leaving it as one partition - this is how the OS expects it to be. This also leaves the most space available on the SSD for your files.
     
  5. hardtofin thread starter macrumors newbie

    Joined:
    Mar 4, 2009
    #5
    Apparently from what i read, you cant partition the SSD only the HDD. So the partition would be on there. I play WoW and am wondering if having this 35gb on my HDD with a partition prohibit it being moved to the SSD even if i used that game all the time? :)
     
  6. Bear macrumors G3

    Joined:
    Jul 23, 2002
    Location:
    Sol III - Terra
    #6
    If it's in a separate partition, it's not part of the Fusion Drive. Only the partition on the HD that's part of the Fusion Drive will benefit from the Fusion Drive.

    You could always get a 128GB (or 256GB) SSD on USB 3.0 or Thunderbolt for files you wanted guaranteed fast access/reads.
     
  7. hardtofin thread starter macrumors newbie

    Joined:
    Mar 4, 2009
    #7
    I see thats very helpful thanks. So, lets say i have a 1TB fusion drive (128gb SSD and 896 HDD and I put the partition 512gb along the drive, is it possible to put some files in the 128SSD + 384HDD part and benefit from the "fusion" tech? Or it doesn't work like that within osx?

    Apologies for all the questions but I don't have this mac yet, I am getting it next week.

    :)
     
  8. Bear macrumors G3

    Joined:
    Jul 23, 2002
    Location:
    Sol III - Terra
    #8
    A Fusion Drive is a Fusion Drive is a Fusion Drive. The HD partition that's not part of the fusion drive will work like a normal HD. I recommend not changing the partitioning.
     
  9. gnasher729 macrumors P6

    gnasher729

    Joined:
    Nov 25, 2005
    #9
    You lose lots of benefits of the Fusion drive by creating two partitions. Your "Home" partition will not benefit from the Fusion drive at all. I very strongly suggest that you stay with one partition, and let Fusion move files and parts of files into the best place automatically. It will be less work for you, there's less chance of you breaking something, and it will run faster.
     
  10. Brian33 macrumors 6502a

    Joined:
    Apr 30, 2008
    Location:
    USA (Virginia)
    #10
    I can't give you a definitive answer, but here's my understanding:

    When you partition a hard disk drive or SSD, you create physical volumes. Two physical volumes (maybe any number, I haven't checked) can be combined to make a logical volume. That's what a Fusion Drive is. I don't think you can partition a logical volume (i.e., a Fusion Drive).

    So, at least in my understanding, you could partition your HDD into two physical volumes, then combine them with the SSD physical volume into a single logical volume (aka Fusion Drive). But the Fusion drive shows up as a single filesystem volume -- you would have no control over where your game (for example) was located among those three partitions because there's just one filesystem per volume (logical, in this case). So there's no point in making the extra HDD partition. However, the game would get to take advantage of the Fusion Drive's SSD speed.


    Instead, you could combine only one of the HDD partitions with the SSD to make a Fusion Drive, and leave the other HDD partition as it's own volume (with its own filesystem). Now you could put the game on the second HDD partition, but it will never get the benefit of the SSD since the SSD is part of the Fusion Drive's (logical) volume, only.

    My advice is to use a single Fusion Drive and enjoy it. The appropriate file blocks from all your commonly used apps and games will live on the SSD, and you won't have to manage a thing yourself. Splitting your storage into OS X and "data" partitions wastes space because you can never know the exact size the OS partition should be (and it's a real inconvenience if it's made it too small so it's usually made too large). It also defeats the "smarts" of the Fusion Drive, because now some frequently-used data resides on a different volume and is ineligible to be moved to the SSD.

    The only advantage I can think of where having two smaller partitions is better than one large one is if you want to use a disk cloning utility to clone the partitions to external drive(s) that are too small to accept a clone of a single larger partition. Even that doesn't convince me because I believe one could software-raid the externals together to make a single larger volume to accept the clone image...

    Well, guess I got a little wordy... sorry! Good luck

    Brian.
     
  11. hardtofin thread starter macrumors newbie

    Joined:
    Mar 4, 2009
    #11
    Thanks for a fantastic response Brian. I will for the the first time in 7 years be using a single partition from now on.

    Many thanks once again.

    hardtofin :)
     

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