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Questions about the new Fusion Drive in the new iMacs

Discussion in 'iMac' started by WizardHunt, Jan 2, 2013.

  1. macrumors demi-god


    I am considering getting a new iMac soon. I need to know whether or not the option with the Fusion Drive will work for me or not. Some advice would be appreciated. Here are my questions below:

    1.) Often I will put too much software on my iMac and will end up reformating and starting over so to speak, but I am not clear how this will affect me when reformating the Macintosh HD. If I order the 3TB Fusion Drive. Is that a 3 TB 7200 rpm HD plus a 128GB SSD? How does one format both of them as one drive?

    2.) The main applications and OS/X is installed on the fusion drive but when the drive is on the desktop, it only shows (on my sisters iMac with a fusion drive) as one single drive. How will I know if I am putting what applications or programs on just the SSD drive or flash drive as they call it?

    3.) I don't want to separate the main HD and the 128GB Flash drive but not sure how this combining works. Can anyone explain it in more detail?

    4.) if the flash drive(128 GB SSD) fails will that kill the drive on the Mac since it is a combined HD setup? If so that does not seem like a good setup at all. Any ideas?

    If you reply to this post, you can reply only to question 1 or 2 or 3 or 4 or all of them.
  2. AT06, Jan 2, 2013
    Last edited: Jan 2, 2013

    macrumors 6502


    1) OSX makes it appear as one drive, and software then sorts out what content to put where (SSD or HDD). Reformatting the drive shouldn't stop this so don't worry. The HDD is 5400rpm.

    2) Again, the fusion software picks what to put where. From the performance people have been getting, it seems very quick and reliable. Software is mainly, if not always, put on the SSD section of the fusion drive.

    3) The software looks at what data is accessed most often - pattern recognition basically. It then chooses what software needs to be put on the SSD section for fast access, and what can be out on the HDD. If something is on the HDD because it isn't accessed often, but then the user begins to access it often, then the software will move it to the SSD.

    4) If the SSD fails, then your fusion drive is pretty dead. Like any drive though, a regular time machine backup should be kept externally.
  3. macrumors 65816

    New question: can I partition the drive and fusion still works?

    I would like to partition my 1TB fusion drive with half for media and the other half for the OS and library.

    Will doing that damage the fusion drive in respect of slowing it all down?
  4. macrumors 6502


    I honestly can't see why it would affect it, although I could be wrong. If it gives you the option to in disk utility, without warning you it could affect the drive, then it should be fine. I would get some more opinions though to be sure :)
  5. macrumors member


    Just like to make a correction, the HDD is 7200rpm. 5400rpm only applies to 21.5" iMacs. As the OP asked about the 3TB option, this cannot be the 21.5" because the highest configurable HDD is 1TB on the 21.5" iMac. I am therefore assuming that the OP is referring to the 27" iMac.
  6. macrumors 68000

    Yes you can do this with a little command line work, i have mine setup just like this. It works perfectly btw.


    This will not be an issue the system handles this. For all intents and purposes you have a single drive that you can format as per normal.

    Once again this is all handled by the sytem automatically, there is no way to know what files are where as Fusion works on a block level.

    Basically all your files are broken up into little chunks (blocks) These are distributed across the two drives so that the most used chunks are on the SSD. For example you may have a 8GB file, 2 gigs of the file that gets used often may be stored on the SSD while the other 6Gb is stored on the HDD as it does not get used often.

    You should have a back system anyway, any disk system can fail!!!
  7. macrumors regular

  8. hfg
    macrumors 68030


    BootCamp can create 1 partition on the hard disk easily ... No Terminal command-line work needed. Once the partition is created, it is no longer part of the Fusion drive and can be formatted and used as you please for "static" OS X data.
  9. macrumors 68000

    Damb i forgot about that, yes you are right. I had to use terminal as i installed windows.
  10. macrumors regular

    1. Yes. I believe you reformat by going through internet recovery assistant. otherwise you download mountain lion from App store and place on USB stick.

    2. All OSX and system files will be on the SSD. The rest you let OSX decide. There is no way at this time to know what is on SSD and what is HDD.

    3. Don't know the details but it's some OSX wizardry. Creates a logical volume combining both on the software side.

    4. Yes if either the HDD or the SDD fail then you're whole system will likely fail. Fail rate is likely very unlikely even given two drive system. SSD probably have a lower fail rate given no moving parts. You should invest in a good backup system. Time machine makes this simple.
  11. macrumors regular


    the OS that come over with the internet recovery is different from the one one the app store at least until 10.8.3 is up I believe it starts 12Cxxxx
  12. macrumors 6502

    Unless you have the 27" iMac with the 3TB fusion drive.
  13. hfg
    macrumors 68030


    My response above was to "spinstorm" who was asking how to do it on a 1TB Fusion. It can be done without Terminal commands and non-destructivly from within the 1TB Fusion environment as delivered from Apple.

    If you look here on the forums there are several threads detailing exactly how to accomplish this on the 3TB fusion. It does require breaking the Fusion drive and then partitioning the 3TB hard disk, then restoring the Fusion join to the desired hard disk partition. This will require Terminal commands and you must backup your data and restore it when you are through. Whether you also install Windows is up to the user ... the partitions external to the Fusion join can be used any way desired.

  14. macrumors demi-god


    This is true, I am only speaking of the 27 inch model as that model only has the 3 TB Fusion Drive option.


    I will have a 2 TB Time machine backup of course. But still i doubt the SSD will fail before the HHD will. That is my guess. But I have many (2 TB) Hard drives that I use for backups. I believe in backups.


    I had boot camp on my iMac once, now I will not use boot camp on my new iMac when I buy it.

    I want to thank you guys for all the responses, you answered my questions and I appreciate it. I will go with the 3 TB Fusion Drive option when I buy mine next month.
  15. macrumors 6502


    Glad to hear you have made your mind up - hope you enjoy it when it arrives :)

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