DIY fusion drive or dual drive combo

Discussion in 'iMac' started by Captdaverobinso, Jan 6, 2013.

  1. Captdaverobinso macrumors newbie

    Joined:
    Jan 6, 2013
    #1
    I have seen a lot of articles on how to make a DIY fusion drive and how it initially performs but I have a couple of questions:

    I have a crucial m4 128 gb SSD which I am planning to install in my late 2011 iMac. My current system is around 80 gb including iTunes and iPhoto libraries, but excluding movies which I keep on a separate drive for streaming around the house. I do some photography but do not envisage a heavy work flow for this.

    Would I be better creating a Fusion Drive to simplify the system or installing the SSD as a boot drive and use the HDD for media files and documents?

    I understand that apparently it is possible to use ZFS instead of HFS+ on Fusion Drives now but as I have been using HFS+ on the HDDs of my previous Macs I don not know if this is worth it?

    I have also read that on SSDs alone, performance degrades as the space is filled up. I understand that Fusion Drives only keep 4 gb free before starting to fill the HDD so does this degradation in performance occur on Fusion Drives?

    Many thanks

    Dave
     
  2. spinstorm macrumors 65816

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    Sep 14, 2007
    #2
    What I have done I think gives me the best of both.

    Why not partition the hard drive to the smallest space possible for the OSX partition.

    That way I can control what is on the SSD and the normal HDD without having to disable it. So I can still keep the speed of the fusion drive.

    Please correct me if you read this and my logic is wrong as I thought it was worth a try.

    I partitioned the drive into a 200GB and 800GB sections.

    I did try to partition it to 124GB but OSX wouldn't let me.

    What that did was leave me with 60GB on the HDD plus the 128GB SSD and all the rest of the HDD as the other partition.

    I then moved my iTunes library to the HDD so the combined usage on my fusion drive/HDD is only 90GB leaving everything on the SSD that I would use most of the time, and in theory the HDD will only be used when I'm watching media which then won't bother me with extra noise as I'll have the speakers on but in normal browsing it should be totally silent...plus I still get the smart caching of files as the fusion is still operating and has some normal HDD space available.

    Does that make sense?
    __________________
     
  3. ConCat macrumors 6502a

    ConCat

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    #3
    Here's how the fusion drive works: It writes to the fastest storage available first, when that's filled, it then writes to the slower storage, however, it keeps 4GB at the end of the faster storage free to speed up future writes, moving data off the faster storage to do so, when it has been idle for a certain amount of time. The rest of the time, it tries to get an idea for which blocks on the disk get used the most, and attempts to keep those specific blocks (not whole files) on the faster storage, and the lesser used blocks on the slower storage.

    In summary: You should definitely use Core Storage to make the most out of your SSD/HDD combo. It's good stuff.
     
  4. js81 macrumors 65816

    js81

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    #4
  5. ConCat macrumors 6502a

    ConCat

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    #5
    What? DIY Fusion Drives? Yes. In fact, I use it with a sliver of my internal SSD and an external HDD to speed things up on the HDD side, so it's quite versatile. I wouldn't recommend it for a server though because there's no option yet for redundancy. If I had to guess, Apple's probably going to make the next Mac Pro completely Core Storage-based, which would probably explain the holdup on releasing the new model. Core Storage is still not feature-complete.
     
  6. Captdaverobinso thread starter macrumors newbie

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    Jan 6, 2013
    #6
    I understand what you have done but I don't understand what the advantage of having extra hdd space with the ssd is, if all media files are on a separate partition because presumably file movement doesn't occur across partitions, or am I mistaken? In this scenario would it not be almost the same as keeping both drives separate?

    ----------

    Many thanks; Would you recommend using it with HFS+ or ZFS then?
     
  7. spinstorm macrumors 65816

    Joined:
    Sep 14, 2007
    #7
    That is the idea as rather than split them with the command line I do have a small amount of HDD space shared with the SSD so I have a bit extra capacity as the back up.

    I accept that it can't move the files to the other partition but I wanted to try and control the content on the SSD without messing around with the core storage, and the truth is if I device I want its full functionality back I can just remove the partition and combine them.
     

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