is Fusion drive now split

Discussion in 'macOS High Sierra (10.13)' started by WayneColo, May 23, 2019.

  1. WayneColo macrumors newbie

    May 10, 2019
    I had problems with the Fusion drive, ended up reformatting it, and reinstalling HS.
    I never actually intended to split the drive, but it looks like I did.
    Now it boots again to HS but in disk utility it shows the SSD as an unmounted APFS Physical Store and diskutil shows this.


    any suggestions as the best way to proceed. I know some try to split the drive on purpose, what advantages would I have to leave it. The more I read about these APFS drives, the more conflicting info I find.
  2. treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    My opinions only:

    APFS is pretty stable now compare to when it first came out. The exceptions to this is Fusion drives on Mojave (updates 10.14.4 and later seem to be more problematical) and on certain Mac Pro hardware configurations. (You can't use Fusion drives using APFS on High Sierra.) APFS is the future for Mac's and it has some nice features. But HFS+ still works and in doing normal day-to-day tasks, there really isn't any difference (the difference comes in configuration flexibility and more efficient use of SSD's among other features).

    You have a small SSD for the fusion drive (28GB, although says you should have 32GB). I'm not sure why Apple even bothered (well, it's probably $) with a SSD that small, considering it looks like you have a 2017 5K iMac. Something like 128GB would have been more suitable.

    Apple wants you to use APFS (vs HFS+) going forward, especially if you decide to upgrade to Mojave. So it will not make things easy if you want to continue to use HFS+.

    Your alternatives are:
    1) Continue to use HFS+ with a fusion drive. It means more work in getting this configuration to work. More so if you want to upgrade to Mojave at some point.

    2) Since you appear to have an external SSD, you can run High Sierra on it with APFS (or HFS+). When you do that, you give up TRIM and SMART attributes. TRIM is more important - some people say very important, others not so much. My opinion is that you should use TRIM if possible.

    3) You can replace the internal HDD with your external SSD - that isn't trivial on the iMac.

    4) You can replace the internal SSD with an Apple or non-Apple SSD - again, not trivial.

    The easiest thing is to just install High Sierra on the external SSD (APFS or HFS+). You can do that without much trouble.

    You would need to decide which option you want and then we can explain what needs to be done to get there. Also, if you want to upgrade to Mojave, now would be an opportune time to do so. The listing of the alternatives above are also abbreviated - if you have further questions, just post them.
  3. WayneColo thread starter macrumors newbie

    May 10, 2019
    Thank you for the response.
    I think the SSD at 28G is basically worthless.
    I'm booting from a external SSD running Mojave now and that is actually running fine.

    I was thinking of moving it back to the "Fusion" drive but with such a small SSD
    and the current state (no longer "fused"), I don't see that it is worth it.

    after yesterday, I'm spooked of screwing things up.
    Since the HD is HFS, can I partition it?
    I'd do that to be able to boot that drive (if I ever needed to)
    and save the recovery HD.
    I'd just abandon the SSD then.
    I don't want to go into the iMac at this point.
    I used to do that kind of stuff, but I'm more of a set it and forget it type now. :)

    If I could partition it, I could use it as an on board backup
    for time machine and/or chronosync.
    that would be a nice alternative as backups would be faster than out to a USB external drive.
    I'm kind of making this up on the fly, but would be really interested if you think it would work.
    Seems to me like it should, but...
  4. treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    I would agree - I don't know what the point is of having a 28GB SSD in a fusion drive, especially for the money that was paid for a 2017 27" 5K iMac.

    Yes, if you're using the external SSD as the boot/system drive, you can partition the HD as you please. If you wish to keep the Recovery partition on the HDD, when you add a new partition, you'd have to take it out of the existing "Macintosh HD" partition that you have - if you re-partition the entire disk, you lose the Recovery partition.

    If it was High Sierra that you previously installed on the HDD, then you have a High Sierra Recovery partition on the HDD. Keep that in mind. Depending on if you used APFS or HFS+ on the external SSD, the Mojave Recovery partitions are a bit different. With APFS, the Recovery partition is really a volume within a "Container" within the APFS partition. With HFS+, it's a separate partition altogether.

    I'm not familiar with ChronoSync but I would be surprised if it didn't allow you to use an internal disk as a backup for the external disk. You should be able to do that with TimeMachine as well but TM is becoming long in the tooth at this point. It wouldn't hurt to have a 2nd backup and use TM for that purpose, but if you have used ChronoSync and find that it works, I'd probably just use that if you wish to only have a single backup. The internal HDD would be slightly faster than an external disk of the same type. Where you would gain speed is if ChronoSync is a well-written, well-maintained, up-to-date backup software (the implication being TM is not).

    If you're just considering ChronoSync as an option but haven't bought it yet, you might want to consider Carbon Copy Cloner. "CCC" (as it's known) can clone the SSD, and keep incremental backups as well. It can also create a Recovery partition on a HFS+ disk even though you are backing up a APFS disk (this action needs to be done as a separate step press-a-button step - it doesn't get created automatically as part of the cloning operation). ChronoSync (and other software pacakges) might do this as well - I'm just familiar with CCC so I mention it.
  5. WayneColo thread starter macrumors newbie

    May 10, 2019
    How do you "take it out"? Never hear of that before. I was thinking of some kind of non-destructive partition (like partition magic, years ago on the PC) Isn't re-partitioning going to erase everything on the drive?

    Right, and I don't see a Recovery Partition on the Mojave external drive. Not sure why or how to fix that either. Can I reinstall Mojave on that drive to create one without losing everything on it? or is that another backup and restore story?

    I bought ChronoSync at least 10 years ago. Its a nice piece of software and is as you describe (well-written, well-maintained, etc) I It appears chronosync and superduper (which I also have) can help with the recovery partitions, but I need to investigate that a bit more. I would like to get a recovery Partition on that mojave disk.
  6. treekram, May 23, 2019
    Last edited: May 24, 2019

    treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    To create a new HFS+ partition from an existing partition in Disk Utility in Mojave:
    1) press Command-2 (or select "View All Devices" from the "View" menu at the top of the screen). You should then have a hierarchy of disks, containers and volumes appear on the left of Disk Utility. If you toggle between pressing Command-1 and Command-2, you can see the difference.
    2) Select the HDD you want to partition (make sure it's one of the items to the extreme left).
    3) Press the "Partition" button.
    4) Press the "+" button towards the bottom left.
    5) A small circle should appear and you can move this around to arrange the size of the different partitions.
    6) Press the "Apply" button when you're done making the changes. Changes are not made until you press the "Apply" button so at any time up to that point, you can press "Cancel".
    There are limitations of how far you can size each partition and this works best when the less full the disk is. This process tends not to work as well when start to add more partitions (3-4-5, etc), in which case other alternatives may be better.

    For Mojave, the default is AFPS and since that's probably what you created, there is no Recovery partition. As I mentioned earlier - with APFS it's a Volume in a Container in a Partition. So it's changed from HFS+. It also doesn't show up in Disk Utility. But it's there. If you use Terminal and use the "diskutil list" command, it should appear. To check, restart your computer, and as it reboots, hold down Cmd-R.

    In looking at the SuperDuper site, there isn't much documentation I can see. If ChronoSync and SuperDuper don't have the capability to create a Recovery Partition for Mojave on your HFS+ HDD, you can download CCC: and use it on a trial (free) basis for 30 days.

    To create a Recovery partition in CCC:
    When you start CCC, there's a sidebar and the first icon option at the top left is going to either be "Hide Sidebar" or "Show Sidebar". If you see "Show Sidebar", click on this icon. On the bottom left should be your list of volumes. Select the "Macintosh HD" (or whatever your main volume is on the HDD where you want to create the Recovery partition). A button on the bottom just to the right of the box of volumes should say "Recovery HD..." Press this button and an explanation box will appear. Press the "Create Recovery HD" button. I haven't actually tried going through this but this should work.

    UPDATE: Since you're going to be doing this later (per your post #7) - I've updated this - making minor clarifications and detailing the instructions on creating (or in your case, updating) the Recovery partition using CCC.
  7. WayneColo thread starter macrumors newbie

    May 10, 2019
    thank you from the time you put into answering my questions. I will try to put this to use this weekend.
  8. WayneColo thread starter macrumors newbie

    May 10, 2019
    I was thinking that I could install mojave on the 28G SSD and store all the data on the HDD part of my ex-Fusion drive.
    But in disk utility, it showed the SSD as unmounted. When I tried to mount it, nothing happens. so I tried to run FirstAid on it. It says an "internal error has occurred, Operation failed.." I assume that means SSD is dead. so Since this is still under applecare, (I just got it), I'm thinking to take it in and if they say they need to go in a replace the 28G SSD, that I will have them put a 500 in instead. I have no idea if they will do that and just charge me for the new drive, but I like the idea.
    If not, I will be implementing treekram's procedures. (thanks again for all that) In the meantime, I'm restoring everything back on my old reliable mini.
  9. treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    Apple typically hasn't done upgrades on the computer it repairs unless they run out of the part that needs repair (which may happen if the part in question is no longer being used in a current computer). But Apple still sells iMac models with the small SSD (24GB and 32GB) so it's unlikely that you'll get an upgrade that way. But you can ask - no harm in that. Since it's under AppleCare, they should repair it if it's broken, though. And if you take it in, you can ask them to restore the fusion drive but my strong hunch is that they'll then put Mojave with APFS with the fusion drive and several people on these forums have reported problems with this so you may not want to go down that route.

    The problem with using (in your case) a 28GB SSD for the OS is that it's difficult to manually manage. SSD's work best if there's some space that isn't used. The OS may also need to create a virtual memory file - you can specify to the OS not to do this or limit it's size but this again part of the management of the small SSD that most people with larger SSD's never have to bother with. There are files and apps you can safely delete but doing that is almost like walking through a mine field. The list of issues to worry about goes on and on. The macOS should be able to manage all of this in a fusion configuration but because of it's complexity, as you have witnessed first hand, even Apple has problems managing the fusion drive.
  10. WayneColo thread starter macrumors newbie

    May 10, 2019
    Right again. I called the shop where I bought and altho they are applecare techs, a repair on this would require it being sent to some apple repair shop. They would only put a 28G back in it. I'm in CO and closest one is in CA. Plus if they were going to be able to swap the SSD for me, I was going to ask that they leave it split. That wouldn't happen either.
    I'm not sure it makes any sense for me to take it in to the shop at all. Just deal with it without that tiny SSD until the Applecare runs out and then put a SSD in there, maybe.. :)

    So currently I have a internal HDD with a fresh install of High Sierra on it.
    Yesterday I put Mojave 10.14.5 on my mini and used TM to migrate the data. It is working properly.
    But I want to get back to the imac monitor.

    I can either migrate the data to the High Sierra disk

    or use the Mojave on my SSD to boot from there
    and use the High Sierra HDD as a backup disk.

    or upgrade the HDD from HS to Mojave and use that as the boot drive.
    No more fusion drives in any case.

    You mention that people are having problems with Mojave on the Fusion drive, I've looked around here a bit and see that. Are there issues with it on a non-fusion drive? I need to pick one. Presumptuous, to ask, but I will anyway. Which one would you pick?
  11. treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    I would not use a HDD as the boot/system drive with either High Sierra or Mojave.

    There were problems that some people were having with APFS on High Sierra early on. I haven't seen those types of problems on these forums recently - except when fusion drives and/or the old Mac Pro is involved. Just have a backup or two in case.

    it's unfortunate that if your SSD is bad that they have to send it out to Apple to fix. While you can't get an upgrade out of a warranty repair, there could have been a chance that your repair folks would have done a HDD-to-SSD swap cheaply since they had the machine open anyway.

    So are you looking to replace the internal HDD you have now? Or replace the external SSD you have now? Opening up the iMac seems like a daunting task to me and you should ask your tech guys if Apple allows them to do a replacement of either at customer request. If you're looking to replace the internal HDD with a SSD, I would go with either a Samsung 850 Evo or a Crucial MX500. The Crucial tends to be cheaper and go on sale more often (the 500GB was recently on sale for $60 on Amazon but the sale is done - it's back up to $67). Performance tends to be less than the Samsungs. If you like premium SSD's, then it would be the Samsung 860 Pro. IMO, cheaper SATA3 drives of this performance class are not worth the price difference.

    If you're looking to perhaps replace the internal SSD or replace your external SSD, then the market dynamics and the technical issues are a bit different - let me know if that's the case and I can give you my opinions.
  12. WayneColo thread starter macrumors newbie

    May 10, 2019
    the internal HDD is High Sierra with HFS currently.
    My external SSD that I'm using to boot right now is a Samsung T5.
    It is running Mojave but not apfs . I have to install a new copy,
    I think that is a bootable backup that has taken over duties
    when everything went south.

    I don't think I need to replace any drive currently.
    an X5 would be nice to boot from, but pricey.

    The tech guys said they couldn't do any repairs under AppleCare. They would just have to send it to CA.

    I can reinstall Mojave on the external SSD and restore the data from TM and boot from that,
    or boot from the HS internal if I can import a Mojave TM backup to a High Sierra drive.
    Just wondering if Mojave is a good choice if its not a Fusion Drive.
    I need to pick a solid setup and straighten out the mess I created in the past week
    when I couldn't boot this thing at all.
  13. treekram macrumors 68000

    Nov 9, 2015
    Honolulu HI
    I misunderstood your question. Sorry about that.

    Other people will have different opinions, still believe APFS to be unstable. You probably won't notice much of a performance difference between APFS and HFS+. There are definite advantages to APFS from a configuration standpoint. Previously you had mentioned about multiple partitions in HFS+. With APFS, you have volumes and unlike HFS+, you don't have to specify specific sizes for the volumes so if you happen to need more space in one volume than you originally thought, as long as the other volume(s) aren't taking up all the free space, APFS will automatically expand the volume size. That's just one example. Just keep a backup or two or three ... - same advice as always.

    If you boot into your High Sierra disk, you may be able to convert the T5 to APFS (you can't convert if you're using the t% as the current boot/system disk). Open Disk Utility, select the T5 disk (left-most, un-indented icon) - then right-click and see if "Convert to APFS" shows up as a non-grey option. If it doesn't appear, select the volume which is one indent in (whatever you've named the T5 to be) and right-click and see if "Convert to APFS" is an option there. It just seems to be hit-and-miss as to what Disk Utility will convert. Otherwise, you'd have to backup, erase the T5, and clone it back or re-install (depending on what you used to do the backup). As I said, I would not use High Sierra on a HDD on a regular basis.
  14. WayneColo thread starter macrumors newbie

    May 10, 2019
    the convert to apfs is greyed out.
    so I will erase and reinstall.
    thank you very much for your insights and attention.

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13 May 23, 2019