Some doubts about Fusion Drive

Discussion in 'iMac' started by iRock1, Mar 12, 2014.

  1. iRock1 macrumors 6502a

    iRock1

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    #1
    Hi there.

    I want to make my own Fusion Drive in my late-2009 iMac (1 TB). So this is the plan:

    I want to replace the optical drive for a 250 GB SSD. Then I will split this SSD into two partitions, one in NTFS for Windows (150 GB) and another one in HFS+ for my little OS X experiment (100 GB).

    Then what I want to do is to make a Fusion Drive merging the 1 TB hard disk and the 100 GB part of my SSD, leaving the other Windows partition in the same SSD alone.

    The result should be two logical volumes, the Windows 150 GB partition in the SSD and the Fusion Drive (100 GB SSD + 1 TB HD).

    Would this work?
     
  2. BayouTiger macrumors regular

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    #2
    I could be mistaken, but I think the Fusion drive needs to encompass the entire drives. I think you can still partition it afterwards but Bootcamp will only use the hard drive.

    From Apple's support site:

    "Do computers that come with a Fusion Drive support Boot Camp?

    Yes. Use the Boot Camp Assistant to create a Windows partition and install Boot Camp. The Windows partition will exist on the hard disk drive, not the Flash drive, and is not part of Fusion Drive Logical Volume Group. 3TB Fusion Drive configurations need to update to OS X Mountain Lion v10.8.3 or later to install Windows 8. See iMac (27-inch, Late 2012): Boot Camp alert with 3TB hard drive for more information."
     
  3. marzer macrumors 65816

    marzer

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    #3
    Yes it is possible. I did this in my 2012 iMac. Splitting the SSD between Windows and OS X fusion drive. When you create the Fusion drive, designate the partitions you want to fused rather than the disk.
     
  4. hfg macrumors 68040

    hfg

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    #4
    Yes .... that will work fine as you described.

    The oem Apple Fusion drive doesn't allow Windows on the SSD because the SSD is too small (128GB) and they don't offer a Fusion option with a larger SSD component.
     
  5. iRock1 thread starter macrumors 6502a

    iRock1

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    #5
    Cool. Is there a mandatory minimum size for the SSD partition that I pretend to use for the Fusion Drive? And beyond that, what would be your recommendation on size?

    Thanks!
     
  6. hfg macrumors 68040

    hfg

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    #6
    I would think that the 128GB would be the minimum practical size since after the 4GB reserved disk write cache, you would see diminishing returns on performance with your environment. I have built my DIY Fusion drives with 256GB to 512GB SSD components, but the optimum size for you would be a SSD large enough to hold your core OS X environment to ensure it was always resident in the SSD to minimize disk access. You would then normally enjoy a almost pure-SSD speed experience and only see disk access for seldom used blocks of data.
     
  7. iRock1 thread starter macrumors 6502a

    iRock1

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    #7
    Some doubts about Fusion Drive


    So following that logic, even a 64 GB partition would do the trick, right?

    From what I've learned the Fusion Drive also moves automatically the most used files (media, documents, etc.) from the disk to the SDD, at least temporarily. So I guess assigning less space in my SSD for the Fusion Drive simply reduces how often and how many of this files will move from disk to SSD.
     
  8. hfg macrumors 68040

    hfg

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    #8
    Well, I wouldn't use a 64GB SSD as they are notoriously slow compared to larger SSDs due to the internal structure. But it would work, if your OS X environment is truly that small. Given the lower costs of SSDs today, I would certainly get a larger one than that!

    Yes, the Fusion algorithms manage how the SSD space is effectively used for your workflow. You would want to minimize that data movement by having enough space on the SSD to experience SSD speeds most of the time. Otherwise, you will be experiencing hard disks speeds ... so why bother with Fusion at all.

    Note that after initial creation of the Fusion drive and installation of your system, it may take some time for Fusion to "learn" your workflow and adjust the files to best accommodate that. Don't just try it for 5 minutes and decide it doesn't work for you. :)


    In your case, I would probably start with a 512GB SSD, divided in half for 256GB Windows and 256GB OS X-Fusion. That would be a smooth running system.
     
  9. deconstruct60 macrumors 604

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    Mar 10, 2009
    #9
    Not a good idea.

    Fusion writes everything first to the SSD. While the low level wear leveling the SSD's Flash controllers may swap infrequently used blocks from the Windows partition for those being hammered by Fusion's target write buffer/utilization, what you are doing with the decrease in partition size is likely driving up that amount of rotation. If there is no Windows partition (the drive max size is 64GB ) then what this does is drive a higher number of writes into a smaller area. Generally not a good pattern for SSD usage.


    SSDs are not extremely fragile but unless the vast majority of the 1TB drive data was store and "forget", 64GB is going to be rather small.




    What you want is a large enough SSD so that the regular "working set" of files that you use over time is smaller than the space on the SSD (or partition in this case). For relatively mainstream workload probably looking at targeting between 10-20% ( about 15% is middle of that) of the drive trying to "tier" data for. So 1TB drive around 150GB.

    64GB is about 6% of a 1TB drive. In the sub 10% zone, you're more likely going to churn the data on the SSD at a faster rate and loose some performance.

    Over 20% probably will get into zone of diminishing returns (unless the working set is much higher than average. )
     
  10. marzer macrumors 65816

    marzer

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    #10
    Boot Camp assistant will not allow Windows to be installed on the SSD portion of an existing Fusion drive. It has nothing to do with Fusion drive itself. I had a factory installed Fusion (128GB SSD + 1TB HD), of which I broke, partitioned the SSD in half and installed Windows on one half the SSD (using Boot Camp) and created a Fusion drive using the other SSD partition and one of three partition I created on the hard drive.

    Screen Shot 2014-03-13 at 12.38.00 PM.png
     
  11. hfg macrumors 68040

    hfg

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    #11
    Right ... but the OP was going to create a DIY Fusion drive (partitioning the SSD first), not tying to install Windows to a oem Apple Fusion drive. Thus, you simply use BootCampAssistant to create the partition, as desired (or Disk Utility), then install Windows normally. You then use the normal DIY Fusion commands to create your Fusion drive with the remaining partition-ID on the SSD plus the hard disk drive-ID.
     
  12. marzer macrumors 65816

    marzer

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    #12
    Hmm, not sure you read my post as you restated exactly what I said. However, to make it clear to those not familiar with the processes of manipulating core storage volumes, it makes no difference whether the machine contains an oem Apple Fusion drive or not. It works the same for an oem Apple or a DIY Fusion drive. And the process I stated is only one way of doing it, there are other ways that don't require the use of Boot Camp. I just find it less of a hassle for my own use.
     
  13. iRock1 thread starter macrumors 6502a

    iRock1

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    #13
    I really appreciate your help, guys. Now it's cristal clear.

    At first I was thinking of buying a 256 GB SSD and destining 128 GB for OS X and 128 GB for Windows. However, I pretend to use Windows for gaming, and being honest 128 GB for that is nothing. I think I'm going to get a bigger SSD and then give around 150 GB (maybe a little less) to OS X and the rest to Windows.

    Anyway, I have one last question. If the size of OS X files and folders increase notably during time, and that SSD partition run out of space, will the new files and folders be stored in the hard disk? I ask because I have several games on Steam, so the Application Support folder is kind of big and I expect it to grow up in the next months.
     
  14. Weaselboy Moderator

    Weaselboy

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    #14
    Yes... the Fusion drive will fill the SSD first then if more data is added it will move the least used data to the hard drive and try to keep the most frequently used data on the SSD.
     
  15. iRock1 thread starter macrumors 6502a

    iRock1

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    #15
    It doesn't matter if it's my personal data or file systems?
     
  16. hfg, Mar 15, 2014
    Last edited: Mar 15, 2014

    hfg macrumors 68040

    hfg

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    #16
    No ... it doesn't matter ... only the frequency of access decides where the files (or parts of files) are stored.

    As for your "Steam Support Folder" concern ... Fusion will not attempt to move the entire folder to the SSD, only the game files you are actually playing may reside on the SSD, the remainder of the folder will remain on the hard disk.

    That is the point of the Fusion concept ... while you might manage your system manually by putting some top-level folders on the hard disk or SSD as you see fit, Fusion manages at a much lower level, only moving small blocks of particular files to the SSD as necessary. It would be impossible to manually manage the millions of files on your system disk to the granular degree that Fusion can perform. This is how they manage with smaller SSD sizes.

    Another example: Your "Applications" folder has dozens of programs in it. You would normally assume that that folder would be best put on the SSD for speed. However, you probably don't actually run most of the programs present in that folder, so putting them on the SSD to just sit and consume space would be wasteful. Fusion may only put the App files you actually use on the SSD, and the remainder may actually be just sitting on the hard disk.
     
  17. iRock1 thread starter macrumors 6502a

    iRock1

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    #17

    I see. Thanks!

    Now that the road is clear, I just have to figure out how to install Windows without a SuperDrive, lol.
     
  18. hfg macrumors 68040

    hfg

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    #18
    If you look down in the "Windows and Linux" forums, you will find many discussions on how to do this. You can purchase a $30 USB DVD reader/burner, remotely attach the optical drive on another Mac on the network, or download or create a ISO windows file on a flash drive.

    Windows can be tricky to install on a Mac, but you will find plenty of solutions in that forum.
     
  19. iRock1, Mar 16, 2014
    Last edited: Jan 28, 2015

    iRock1 thread starter macrumors 6502a

    iRock1

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    #19
    The USB reader/burner and flashdrive options are a no-go in older Macs. I can guarantee it to you. ;)
     
  20. iRock1 thread starter macrumors 6502a

    iRock1

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    #20
    Oh, another question. And this time I really expect it to be the last one. :D

    If I decide in the near-future that I want a third OS (say Ubuntu), could I safely undo my Fusion Drive (i.e. without losing data) to create a third partition in the SSD for Linux, and then do my Fusion Drive again?
     
  21. hfg macrumors 68040

    hfg

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    #21
    You will have to have a good backup of the Fusion contents since it will be destroyed when you break the join. Then create another partition on the SSD (hope you have a large one) for your Linux. Then, do as you initially did to create a new Fusion with the SSD-PartitionID and the HD-DiskID. Once that is done, restore your backup to the newly created Fusion drive and you should be back where you were, only with a Linux partition on the SSD.

    I do have a nagging concern for which someone can hopefully add additional information. I recall Windows boot has a issue with the number of partitions it will search across to find the installation (4 I think). This may be a problem which, if encountered, might be solved by the order of the partitions on the single disk and which is used by Windows.

    Good luck ...

    -howard
     
  22. iRock1 thread starter macrumors 6502a

    iRock1

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    #22

    In that case perhaps it's a good idea to make three partitions since the beginning, even if one of them will remain unused for some time. Truth is I just want to install some Linux's distribution to learn about it and not much more. Probably something around 50 GB or even less will do the job.

    I'm intrigued by what you've said about Windows though. You never know when a new partition is going to be needed, and I count four already (OS X, recovery, Linux and Windows).
     
  23. hfg macrumors 68040

    hfg

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    #23
    I think you have to count the "EFI" partition in there as well. :)

    You could possibly run your Linux distribution as a "virtual machine" under VMware Fusion or Parallels. They may even have already configured installations available for download. I use VMware Fusion with Windows7 and Windows8.1 with no problems. I also have bootable Windows (BootCamp) which I can also access from VMware in OS X so that I only have a single Windows installation with applications. Works very well either as a vm or booted.
     
  24. iRock1 thread starter macrumors 6502a

    iRock1

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    #24
    Well, virtualization for Linux sounds like a good idea, but I'm not sure of how much resources I'd need in the future – maybe I'd need to boot from a Linux partition because virtualization won't be fast enough for certain tasks.

    What you've said about Windows worries me though. What if I want to beta test an early release of OS X? Obviously I'd want to create a new partition for that.

    BTW, what do you mean by the EFI partition?
     
  25. hfg, Mar 21, 2014
    Last edited: Mar 21, 2014

    hfg macrumors 68040

    hfg

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    #25
    EFI = Extensible Firmware Interface

    Some information can be found here:
    http://en.wikipedia.org/wiki/EFI_System_partition

    It is a 200MB partition on your disks. If you open Terminal and enter the command "diskutil list" you can see it on your system.


    This article discusses the 4 partition limit:
    http://www.twocanoes.com/support/wi...-tb-or-larger)-drive-in-lion-(10.7)-and-later
     

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