n00b help...disable Fusion/separate SSD and HDD

Discussion in 'iMac' started by jman995x, May 24, 2013.

  1. jman995x macrumors regular

    Sep 8, 2007
    I've been reading some posts regarding disabling Fusion and creating separate SSD and HDD volumes.

    I literally just unpacked my new iMac about an hour ago and want to do this before anything goes onto it.
    My goal is to have the 128GB SSD be ONLY for booting and applications (which I will, of course, make a BootClone of once it is set up)....and have the rest of the space in the Fusion HDD be for non-boot, non-app files (pix, mp3's, etc.).

    Having said that, I'm only following about half of the discussion in some threads and was hoping that someone could give me a step-by-step on how to separate completely my Fusion into a distinct SSD boot drive and HDD drive (and not have the OS transfer things to-and-fro unless I tell it to). While I'm not well-versed in Terminal commands, if somebody shows me what to do/type, I'm more than willing to dig in and get my hands dirty....there are just a lot of things that seem to be common knowledge to some of you on the forum that gets glossed over (and I don't want to miss any steps that are assumed that I already know...which I might not).

    From some of the threads I've read, some of you are doing exactly what I want to do in just a matter of minutes...I just want to make sure I have all of the steps so nothing gets screwed up.

    Any help would be great.

    Thank you all for your time.

    Best regards,

  2. Hirakata macrumors 6502


    Mar 17, 2011
    Burbank, CA
  3. benwiggy macrumors 68020

    Jun 15, 2012
    Why not let the OS put the files where they will benefit you most? There's probably a lot of system files that you will rarely use. There's probably a lot of blocks of app data that you will never use. There's probably a lot of user data that might benefit from being on the SSD. With Fusion, CoreStorage will sort it out for you.

    There are particular usages for which Fusion might not be best, but I don't think you've outlined one.

    Not evangelising: just trying to save you the bother of splitting the drive and managing your files, and giving you the benefit of Fusion performance.
  4. jdblas69 macrumors regular

    Aug 15, 2012
    I'm with benwiggy...

    Not sure why you would want to disable the fusion drive. I realize some people like to have control over where their files go but why not try it out, it is designed to give you the best of both worlds.
  5. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    The OP's question was already answered, so I wanted to ask a more general one: When people go to the expense of buying an SSD and installing it as a boot drive, why on earth do they go to so much trouble to avoid putting their smaller user files on it?

    It's obvious why you wouldn't want your iTunes folder there, and most couldn't afford the storage for their photo library, either, but to me spending that kind of money for an SSD and then taking my mail folder--a folder with 20,000+ very small files in it that only take up a few GB but are read, indexed, searched, and frequently updated by a program that is open 100% of the time my computer is on--and putting that on a rotating hard disk seems like complete insanity. Mail is nearly the perfect use case of an SSD. I'm not going to buy something designed to make Mail run way better, then not use it for that.

    Same goes for most of the contents of my ~/Library; it's a lot of small random-access cache and prefs files that will benefit whatever app I'm running at least a little, and don't cumulatively take up much space. The perfect use case for an SSD. Why would you go to the considerable home-folder-moving effort to not put that on your SSD?

    Personally, both of my home computers have 120GB aftermarket SSDs (didn't want to hack Fusion), and I have my user folder in the default SSD-boot location on both--I just store media on a separate rotating drive. Didn't require any hacks or Unix fiddling, I just moved the iTunes and iPhoto libraries, and don't store big stuff in the default folders. Both have plenty of free space, and run extremely fast, without leaving me wondering if relocating ~/ or my library is costing me any performance.
  6. jman995x thread starter macrumors regular

    Sep 8, 2007
    I guess I'm a little confused then.
    I've read a couple of different things regarding SSD's and was trying to avoid all of them:
    1. I've read that the Fusion drive will completely fill up the SSD before it starts putting files on the HDD. In my past experience, when a drive reaches its capacity or even gets close, it starts losing performance. Is this not the case with SSD's and if so, why not?
    2. I've also read that SSD's have only so many "writes" that they can perform, then they turn into a read-only paperweight. What I was hoping to do was have my SSD drive be my boot drive and apps drive so that there isn't a lot of writing going on (thus prolonging the life of the drive). Was what I read about SSD's only having so many write cycles in their lifespan not correct?

  7. gnasher729 macrumors P6


    Nov 25, 2005
    Simple answer: Don't.


    1. Hard drives lose performance when they get full. That's because the drive is a rotating disc, and at the outer edge of the disc you have more inches per rotation than closer to the centre, so more bytes per rotation, so more speed. That's why some people buy 3TB when they only need 1TB. But this applies to hard drives only.

    2. SSD has only a certain number of writes. That number is _huge_.

    Just apply some common sense. Whatever you read, do you think the guys at Apple haven't read that? And haven't read just some articles on the Internet, but have talked to the people at the SSD manufacturer who actually _know_?
  8. adb1973 macrumors newbie


    Aug 25, 2008
    wise guys...

    Off topic: Why do some people here at MacRumors just don't answer questions properly? Let the OP 'break' his Fusion setup if he wants too. Just answer his questions, AND after the how to give your 'advice....'

    That being said....

    If you really want to do this (because you want Windows on your SSD too for example or because you are afraid of the radiation a Fusion drive might give you)

    1. Breaking the fusion setup...
    a. boot into recovery mode holding R or boot from a separate HD
    b. open Terminal
    c. type diskutil cs list
    d. copy (command-c or mouse) the large number after Logical Volume Group
    e. type diskutil cs delete [large copied number]
    d. you just destoyed you fusion drive setup
    e. close terminal (type exit)
    f. open DiskUtility and partition your Drives the way you want

    2. Fusion filling up the drive completely...
    True, but cleverly Fusion leaves a certain portion of the drive untouched to prevent this behaviour AFAIK it's about 4gb but i'm not entirely sure about the size

    3. what you read about the life cycle of SSD's was correct. But as said before the number of writes is huge. It'll probably take 5-10 years before you notice anything and error correction or diagnostics give you warnings beforehand, your hd might fail earlier...

    that being said:
    - see Fusion drive as a chain, as soon as one part (HDD or SSD) breaks your Fusion drive, your data is lost, period. so be sure to have a working TimeMachine backup.
    - repair wise it's two parts so if one thing fails you don't have to replace both

    my 2 cents: i've chosen to turn my SSD+HDD setup in a DIY Fusion Drive because i think the advantages are bigger than the disadvantages.
    The only thing i hate is that apple puts the boot camp partition by default on the slower HDD which i personally think is something a user should be able to descide on it's own. making a DIY FD you are able to bypass that and install windows on ssd too. i haven't tested that yet btw.
  9. Apple fanboy macrumors Penryn

    Apple fanboy

    Feb 21, 2012
    Behind the Lens, UK
    Now why did you go tell him that! :D
  10. G-Mo macrumors 6502


    Nov 6, 2010
    Auckland, NZ
  11. gnasher729 macrumors P6


    Nov 25, 2005
    Why do some people here at MacRumors refuse to answer people's question, and instead insist on replying to their posts? When the question that someone posts is clearly not the question they actually want to ask, it would be small minded to reply to the post and not answer the real question.

    Extreme: If someone asked you about the best method to kill themselves, would you tell them about the best method, or would you try to find out why they are asking?
  12. adb1973 macrumors newbie


    Aug 25, 2008
    Peace, understanding and Fusion Drives...

    Ah, thx! I understand! So if a woman asks me to come to her house for a cup of coffee and a chat she actually means she wants to have sex with me :D and I must answer to that never asked question?

    Come on, breaking your Fusion Drive is by no means the same as committing suicide! As long as there's no real life danger involved we should all be answering questions not giving advice only [end of preacher mode]

    I'm actually considering breaking AND rebuilding) my (soon to arrive) original fusion drive to force the system to leave a space for a NTFS or EXT4-partition on the SSD. I assume (at this moment) that will in no way:
    - harm my fusion drive (CS array)... but i will let you all know when it does
    - kill me... but i'll ask other people to let you know when it does :rolleyes:
  13. gnasher729 macrumors P6


    Nov 25, 2005
    You know, and I know, and everyone reading this knows, that you are deliberately misinterpreting what I was saying. Do you think you are winning any points that way?
  14. leman macrumors G3

    Oct 14, 2008
    Given that OP's question was answered in the beginning of the thread, I would like to add my voice to the 'don't do it'. You won't be win anything, but you will lose performance and gain additional headache as you'll need to manage the two volumes. In the end, you will only worsen your user experience. Save for some specific usage cases (such as working with very large data sets), the Fusion Drive will do a MUCH better job managing your data then you will be ever able to.
  15. adb1973, May 26, 2013
    Last edited: May 27, 2013

    adb1973 macrumors newbie


    Aug 25, 2008
    My last post indeed was a bit sarcastic and probably not giving me any 'points'.
    Let's stop it since we both have made clear our points. We might have a bit of a difference in opinion. I think apart from the OP there's hundreds op people watching this and a small 'how to' comes in handy and saves them some time.

    Is it stupid to break your (original) Fusion Drive Setup?

    Basically it's like this (please add to this if you feel up to it)

    Reasons to BREAK your Fusion Drive Setup:
    1. 100% control about what's on the SSD and what's not
    2. possibility to put Windows/Linux on your SSD*
    3. better overall SSD performance possible
    4. better data-retention/repairability
    5. bigger 'free' space area to increase performance (apple saves 11,7% AnandTech recommends 25%, see 1 month with Apples Fusion Drive)
    6. possibly an increase of SSD lifespan
    7. editing large HD-videofiles and graphics from internal SSD
    8. increased gaming performance

    Reason NOT TO BREAK your Fusion Drive Setup:
    1. Flawless everyday operation
    2. 100% usage of your fast hardware (minus 11,7% 15GB)
    3. a no brainer if you don't have certain special (professional?) needs
    4. the OS makes the decisions
    5. fully supported setup with no known glitches (exept for 3TB BootCamp problem)

    * I personally see this as an Apple Marketing strategy not as an hard- and/or software necessity.
  16. themcfly macrumors regular

    Jul 20, 2011
    Ill' add to that:

    • The fact that if your HDD fails while on FD, your machine is completely unusable, and you just have to take it to the Apple Store to get it fixed. While unfused, you can simply boot into your SSD and work your files off your backup, until you have the chance to take that in for a repair.

    • The ability to format/update your boot operating system without having to move all your data. Maybe you just want to start fresh and re-install 10.9 the day it comes out, while unfused you can.

    • Extend the lifespan of your HDD: if you simply know where you want your files to be you don't actually need the system to move them back and forward following your usage patterns. For example, I don't need a 1080p video to be on the SSD because the read speeds are perfectly fine on the HDD and the access time is neglectable. I just want my software on the SSD.

    We're not saying that Un-Fusion is the only way to go, but it makes sense for a lot of reasons. So it's pretty annoying to come here and read posts of people thinking that their needs are the same of everyone else's.
  17. WilliamG macrumors G3

    Mar 29, 2008
    No kidding. I separated the fusion disk in December and would never go back.
  18. Gav2k macrumors G3


    Jul 24, 2009
    Just on point one. Data read from the outside of a platter transfer's faster due to the blocks passing under the head at a faster rate.
  19. Nuke61 macrumors 6502

    Jan 18, 2013
    Columbia, SC
    Breaking it up doubles your backup requirements.
    You paid $250 for a 128GB SSD
  20. Fishrrman macrumors Pentium


    Feb 20, 2009
    To the original poster:

    Have you attempted to "un-fuse" your drives yet?

    If you're still thinking of this, some suggestions:

    1. BACK UP the contents of the computer FIRST THING after you take it out of the box. You may need to create an account first, but I suggest that you create an "empty" account (that is, don't "migrate" from your older computer, not yet).

    Use CarbonCopyCloner (you can use it free for 30 days from downloading) to create this "clone" of your "next-to-virgin" software.

    2. Boot the iMac from your cloned backup

    3. UN-fuse the internal drives. You'll need the terminal commands to do this.

    4. Now that you have the drives "split", I would further suggest that you partition the HDD into as many "pieces" as you think you'll need. I would recommend that the FIRST partition be a little "under" the size of the SSD. You can use this to create a "cloned bootable backup" of your SSD that will always be available to you in an emergency.

    NOTE: there's another good reason to have a bootable partition on the HDD. That is -- if you split the drives, and later boot from the recovery partition, and then launch Disk Utility, it will automatically attempt to RE-FUSE the two drives, wiping out everything that's on them. It WON'T do this if there is a second partition "present" that has a copy of the OS already on it.

    Use the rest of the HDD for whatever you wish.

    5. Now, with your internal drives set up as you wish (but still "empty"), it's time to get your data onto them.

    First, while still booted from the backup clone, "RE-clone" the contents of the backup clone back to the SSD.

    6. Now, boot from the iMac again (disconnect cloned backup if necessary), to be sure you get "a good boot".

    When you get to the finder, it's time to start "migrating" from your previous computer or backup drive. You'll probably want to bring over apps and your account, but be aware that if you kept a lot of files (music, movies) in your home folder, that they will go into the home folder on the SSD. You may need to move these manually later.

    I would put away the "original clone" of your factory-fresh copy of the OS for safekeeping. You might need it again someday.
  21. benwiggy, May 29, 2013
    Last edited: May 29, 2013

    benwiggy macrumors 68020

    Jun 15, 2012
    If the SSD fails, in either scenario, you would have to boot from another drive, or install the OS on the HDD and restore your data.
    You should expect devices to fail, and be prepared with backups and alternative boot drives whether you have Fusion or not. A RAID 0 would also fail if one of the disks failed.

    Default installation of OS X does not require moving your data. I've installed every version of OS X from 10.3 onwards onto a drive containing my user data.

    I'd want to see some data correlating the lifespan of an HDD and "having your user files on a separate volume". Surely, if CoreStorage is putting your least used data on the HDD, that would bode well for the drive's lifespan?

    On the flip side: There are some user files that would be best stored on an SSD rather than an HDD. Email mailboxes, for instance. User caches. SQLite3 databases. All sort of other things. And indeed there are some system files that would work just as well on the HDD.
    The beauty of Fusion is that it can sort blocks of data between the drives and still maintain the necessary file hierarchy. So two files in the same folder could be on different drives. In fact, blocks within those files could be on separate drives.
    That's a level of sophistication you can't match with the broad stroke of "user files: HDD; System files: SDD".

    Each method has particular characteristics that may be preferable to a particular user. No one, I would hope, is saying "do this, or you're stupid". However, giving as much information as possible on a novel technology allows people to make a better choice for them.
  22. hfg macrumors 68040


    Dec 1, 2006
    Cedar Rapids, IA. USA
    There is, of course, the option of putting 1 additional partition on the Fusion drive per Apple documents. Normally, this might be used for a BootCamp Windows installation, but you can use it however you wish. You can make this partition the size you need, and move the "stationary" files you don't wish to be managed by Fusion over to this partition, where they will sit, unaffected by the Fusion drive algorithms. The remainder of your OS X environment will be block managed by Fusion.

  23. adb1973 macrumors newbie


    Aug 25, 2008
    +1 for this and all the other things you wrote in your reply
  24. Makosuke, May 31, 2013
    Last edited: May 31, 2013

    Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    The discussion has already moved on, but I just couldn't let this bit sit un-corrected.

    The read rate on a rotating hard drive does decrease as it reaches full (which as already pointed out is the inner track, not the outer--the outside edge is fastest due to higher linear velocity under the head), but that is not the main reason that rotating drives get drastically slower as they get nearly full.

    The main reason for that is fragmentation; as free space approaches zero, the drive is usually forced to use whatever bits and pieces of free space remain to store files, which often results in severe fragmentation. This is mitigated somewhat by defragmentation, but the fuller the drive is, the harder defragmentation is to do effectively for the same reason--there's nowhere to move the files to consolidate them. The end result is that the drive usually ends up seeking around a lot to read or write data, which drastically lowers speed on a rotating hard drive. The familiar grinding sound of a thrashing hard drive is a symptom.

    SSDs, on the other hand, don't have a head that moves--they have static blocks of data on chips, and the read rate for "fragmented" data (which is an entirely different and semi-meaningless concept on an SSD due to the way they internally manage data blocks) is exponentially faster than for a rotating hard drive. A large hard drive would be lucky to manage 200 random read operations per second; a good SSD might do 20,000. They still may have problems when nearly full, but not for the same reasons, not in the same way, and often not to the same degree.

    And, as mentioned, Apple accounts for this--Fusion leaves a sufficient buffer to address any performance issues.

    Some real-world numbers might be useful:

    Most consumer SSDs use MLC NAND, which should have at least 3000 write cycles per block before failing. They also have some over-provisioning (extra storage kept free to replace failed blocks) built-in, and do wear-leveling automatically so that the same block isn't written to repeatedly while others are unused. On a 128GB SSD, you should be able to write around 380TB of data before chips start to fail that it can't compensate for.

    Assuming a conservative 3x factor for the drive moving data around internally, that still means about 128TB of data. That works out to 1GB of data per hour, 24x7, for 14.5 years. I seriously doubt the computer will be in use that long even if the rest of the electronics in the drive somehow survive 15 years of use.

    Bottom line: Some people could conceivably wear out an SSD. High-write servers definitely might (which is why they use SLC chips in enterprise SSDs). The average consumer, however, will not.

    I would, of course, be happy to be corrected if I've made any technical errors.

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