Very slow boot on Fusion and Big Sur

Your drive is working fine, as it should be.

The structure goes Physical Storage (Fusion Drive) > Container (APFS) > Macintosh HD (System data, with snapshot) > Macintosh HD - Data (user data).

For more speed, you really need that external SSD.

If you need more help, please start a new discussion form, as this discussion form is already quite long.

Cheers,

Jack

No one from this thread has ever uploaded an EtreCheck report. No one is giving it a chance to help. I agree that EtreCheck is the next step to do here, as it can find potential issues as to why boot times are slow.

Cheers,

Jack

Thank you, Tomeranaray, this is the kind of feedback that potentially helps a lot of people, who are willing to start from scratch with Big Sur. I wouldn't call it a solution as the procedure is far from what most users would be comfortable with, and a real solution would be that a live upgrade from a previous OS to Big Sur delivers the same result: a boot time around 30 seconds.

Just like you, some months ago, I did a clean install of 11.1, resulting in a boot time of less than 20 seconds but only before installing any apps like Pages, Numbers, Keynote, and iMovie. After installing just those, right from the App store, my boot times tripled, and adding Photoshop and Lightroom, once again went up to over 2 minutes. It seems that adding more apps and data "on top of" Big Sur made the OS decide it needed much longer and unacceptably long boot times.

I've got a few questions for you, related to this last remark of mine:

1. Do you have any third-party apps like Photoshop and Lightroom Classic or similar, and have you re-installed them already?
2. Did you re-install apps like Pages, Numbers, Keynote, iMovie, Garageband...?
3. What is the current size of your Music and Photos libraries?
4. How much free space do you now have on your Fusion Drive (it's a 1TB, isn't it?)?

Big Sur demands APFS on all internal drives, so yes to the first part of your question.

On which part of a Fusion Drive (fast but small SSD or slower but large HDD) resides what and when, is totally invisible to the user and is totally dependent on the logic (software) that manages the Fusion Drive. In the past there were Terminal commands one could use to see which part of the FD was being written to when e.g. saving larger files, but I am not sure that Big Sur still allows these commands to be executed or gives the feedback they ask. The software that manages how the OS, the apps, and the data are spread out over the two parts of the Fusion Drive (not even as complete files but on block level!) probably works quite like the software that manages RAID-systems, but with an extra layer of intelligence that normally gives preference to writing and keeping the apps and data that are most often used, onto the SSD blade (because it's faster than the HDD to read from and write to). That means that bits and bytes are being swapped almost all the time from HDD to SSD and vice versa whilst we use our iMacs. The problem with Big Sur seems to be that, until now at least (I haven't had the opportunity yet to test out 11.3 as you have had), during startup (boot) the OS was constantly reading and/or writing a number of very large and essential parts of itself from and to the HDD, and not (or only partially) from and to the SSD part of the FD. Catalina never had that problem and considering that Big Sur itself is much and much larger than the Catalina OS, it seemed that Big Sur until now could not or would not use the SSD for those essential parts to reside on during the boot procedure. It had to use the slower HDD for that. 11.3 seems to have found a solution for that, but there are other users upgrading or updating to 11.3 and reporting absolutely no difference with boot times still up to 3 minutes...

While I did suffer from the issues mentioned here, I do recommend updating to get the latest features and security patches. I assume the performance issues are not that widespread so your chances are pretty good (I do not have any data on that but imagine that the issue would be more prevalent in the media if every single fusion drive was affected).

I only had my issues fixed after doing a clean install (including running resetFusion) of version 11.3 but the poster above had no such luck so it’s not a guarantee.

The simple truth is that you are not able to understand the difference between what constitutes the "Fusion Drive" inside an iMac. It consists of 2 parts, not one.

I am wrong? Prove it, by using "System Information" and do what I told you: to check both items in the Hardware section.

Disk Utility shows you not one SSD but one drive: the fused drive, consisting of 2, physically separated parts, that are installed in 2 different places on the iMac's motherboard. Have you tried to see what "System Information" tells you? No? Then I would advise you to stop insulting me.

Can you please enlighten us all and tell us what your "original Fusion Drive" looked like when it was removed (replaced) in your presence? If it was only one part, the original HDD, then I am right in explaining you for the umpteenth time the difference between a "Fusion Drive" and the HDD part of a "Fusion Drive". A "Fusion Drive" is not even a physical drive, but a sort of "upgraded" RAID system, consisting of 1. an SSD blade (installed deep inside the iMac, which makes it a whole lot of work to physically remove it) and 2. a conventional HDD.

If you refuse to tell us what "System Information" is showing in the two sections of the Hardware (NVMExpress and SATA/SATA Express), then it is someone else who is living in a castle on a cloud...

What your original HDD is doing now, is of no importance to what I said above. Or actually it is, because you don't say anything about the SSD blade, which is the other integral part of the "Fusion Drive", being removed...

Until I see a screenshot of the two sections in System Information, described above, your Fusion Drive iMac is still a Fusion Drive iMac, as only the HDD part of it has been replaced by an SSD - as is usual. Removing the SSD blade would make no sense as it most probably would render your iMac's motherboard dysfunctional.

The only reason why I still reply to your insulting comments, is because you are not the only user here and your comments make their problem even more complicated than it already is. Replacing the original 1TB HDD with an expensive 1TB SSD is not a solution, it's a work-around, and a very expensive one. The solution for the problem with Big Sur booting in 4 to 5 minutes on recent 1TB Fusion Drive iMacs, is - as I was told by a senior Apple engineer working on the problem - to rewrite parts of the OS. I hope they will do it successfully.

Are you willing and able to answer my questions and show us screenshots of the "System Information" hardware sections (NVMExpress and SATA/SATA Express)? I hope you do.

1. I installed Big Sur from scratch.
2. 11.2.3
3. the login screen appears 7 seconds after pushing the power button. Then, after typing the password, it takes about 52 seconds to get the desktop. I've FileVault on.
4. The most used applications (in my case Safari and Mail) are quite responsive just after the desktop rendering is completed, but they're not as fast as when booting from the external SSD, of course.
5. I've Office suite, not Apple applications

BTW: I try to keep my booting process as clean as possible. After installing something, I usually remove the autolaunch components, if they're not stricty necessary.

Here I'm talking about the booting time only. Starting the biggest applications always takes some time (many seconds ot tenths of seconds). It's clear that Fusion drive is an outdated technology, but my iMac is still usable and considering it's a six years old hardware, I assume I have to accept it. Just booting from a cheap external SSD (12 € enclosure + 60 € 512 GB SSD), makes everything much faster (but not the booting process, because the recognition of the external drive at the beginning takes some more time).

Thanks for the info!

Whatever the cause of the problem, it's definitely a complex issue. And it's important to consider that, although most of the users with this problem of incredibly slow boot times, have a Fusion Drive iMac (from 2015 all the way up to the 2019 model), we are using different apps and have different amounts of data on the Fusion Drive and/or in the iCloud.

Your 1TB Fusion Drive is pretty much "empty" compared to mine (I have over 470 GB free), so that could definitely be a big help to Big Sur on your iMac.

So far, both you and Fabio_V, seem not to have installed any larger third-party apps like Photoshop or Lightroom Classic. Yet, like I said above, a few months ago, installing 11.1 from scratch, allowed me to have a boot time of 20 seconds into the desktop. But at that moment, my account was new (no migration yet) and virtually empty. Installing Pages, Numbers, Keynote, and iMovie instantly made the boot time two or three times as long... Re-installing Photoshop and Lightroom, and connecting to the iCloud made the boot times go up to three minutes again. However, once everything had found its proper place, launching every single app and using it was very fast.

And yes, in your case, only time will tell what will happen once you add more data or more apps.

Whatever it is, there seems to be some kind of threshold of data being swapped around between the HDD and SSD parts of our Fusion Drives that defines if Big Sur is able to start up in a reasonable amount of time or not, and the "logic" of the software behind that apparently cannot be adjusted or managed easily or correctly by Big Sur.

You're right about the APFS part, I forgot about that and confused it with APFS for Time Machine support that only came more recently...

I've read that the SSD part of Fusion Drives always has 4GB free as a designated landing place for active read/writes, and only later files are moved to the HDD part in the background, thus guaranteeing fast speeds. The OS itself should also remain on the SSD. So your experience that boot times temporarily went up after installing Photoshop is a weird one.

I have now reinstalled iWorks and Xcode, in addition to MS Office, and rebooted in between every additional installation, and at no moment were boot times affected. I can only conclude that a faulty Big Sur installation either puts crucial parts of the OS on the HDD drive and/or the 4GB free space on the SSD is no longer intact and every read/write operation occurs on the HDD part instead.

If you run "diskutil list" from the terminal prompt, you can see the configuration of your Fusion Drive. As you can see I have the 24GB SSD version. I do notice that the Macintosh HD⁩ volume (which contains the OS) is 15.3GB, so (while it's hard to conclude this from the output as it's unclear what is stored on which drive), there's at least theoretically room left on the SSD for the 4GB landing zone and some additional frequently used files.

But the fact remains, we will never know what is stored where, and when the OS decides to move files based on what criteria.

/dev/disk0 (internal, physical): (SSD part)

   #:                  TYPE NAME                    SIZE       IDENTIFIER

   0:      GUID_partition_scheme    *24.0 GB    disk0

   1:                 EFI ⁨EFI⁩                     314.6 MB   disk0s1

   2:                 Apple_APFS ⁨Container disk2⁩         23.7 GB    disk0s2

/dev/disk1 (internal, physical): (HDD part)

   #:                       TYPE NAME                    SIZE       IDENTIFIER

   0:      GUID_partition_scheme                        *1.0 TB     disk1

   1:                        EFI ⁨EFI⁩                     209.7 MB   disk1s1

   2:                 Apple_APFS ⁨Container disk2⁩         1000.0 GB  disk1s2

/dev/disk2 (synthesized): (full Fusion Drive)

   #:                       TYPE NAME                    SIZE       IDENTIFIER

   0:      APFS Container Scheme -                      +1.0 TB     disk2

                               Physical Stores disk0s2, disk1s2

   1:                APFS Volume ⁨Macintosh HD - Data⁩     186.1 GB   disk2s1

   2:                APFS Volume ⁨Preboot⁩                 285.0 MB   disk2s2

   3:                APFS Volume ⁨Recovery⁩                622.1 MB   disk2s3

   4:                APFS Volume ⁨VM⁩                      1.1 MB  disk2s4

   5:                APFS Volume ⁨Macintosh HD⁩            15.3 GB  disk2s5

   6:              APFS Snapshot ⁨com.apple.os.update-...⁩ 15.3 GB    disk2s5s1

Unfortunately, my 2019 27inch 5K iMac (i5, 3,1 GHz) with 40 GB of RAM and a 1TB Fusion Drive is still taking a full 2 minutes to get to the desktop and then I still have to wait another minute or so to be able to have apps start up quickly. Once 3 to 4 minutes have passed since the Apple startup logo appears on boot, everything runs smoothly and very fast. It's the boot time that is still absolutely abnormally long.

I have done the following:

1. A straightforward, in-line upgrade from Catalina to Big Sur 11.3, which gave no issues concerning potential loss of settings or data. Several bugs from previous versions of Big Sur seemed to have been ironed out. Boot times, however, remain a problem. Up to three minutes to have a responsive system.
2. A clean install, having "erased" all internal volumes and reset the Fusion Drive. When asked to migrate during Setup, I used a external drive which is a clone (a ChronoSync "mirror") of the non-system part of the Fusion Drive ("Macintosh HD - Data"). Alas: exact same results as above: same long boot time but no issues concerning settings, apps, or data - they were all nicely migrated.

What I haven't done yet, is a clean install, creating a new user account, and re-installing my apps and data from scratch. I'm not keen on trying that because the whole procedure is so time-consuming without any guarantee that it would yield normal boot times.

Apart from that, I have noticed something in the screenshot that Tomeranaray has posted with the results of the "diskutil list" command in Terminal. It could be meaningful in trying to pinpoint the cause of the problem on my system, but I doubt it for now. The SSD part of the Fusion Drive on his system is given the device ID "disk0", the HDD part is "disk1". On my system it's the opposite. When I ran the "diskutil resetFusion" command when starting procedure #2 above, the feedback in Terminal was actually correct and identified my "disk1" as the SSD part and "disk0" as the HDD part, saying the first was the fastest part of the Fusion Drive.

Could you, dear Fabio, run that command on your system, please, and post the result here, or simply give the respective device ID's of the two separate parts of your Fusion Drive?

Yes, thank you. I already did that a few months ago, with a previous version of Big Sur. It didn't change anything to the boot time. I may try it again on 11.3, or actually since this morning 11.3.1 already...

I've really checked everything I could concerning my account, even displaying potentially disturbing hidden files and folders. Nothing seems to be wrong.

As I said, with 11.3 boot time has improved on my system also, but only marginally. As soon as I added apps and data to the newly created account, the boot time went up, from around 25 seconds to 2m30s or more before having a responsive desktop and Finder. I have about 520 GB of free space left on my 1 TB Fusion Drive. That's certainly not a problem, but it is far less than what you and Tomeranaray have stored on your iMacs. As I have reported a few months ago, with a previous version of Big Sur I was also able to boot my iMac in 20 seconds, with a newly created, empty account, but simply adding a few apps like Pages, Numbers, Keynote, and especially iMovie made the boot time climb up to 1 minute or more immediately. I am starting to think that there is some kind of threshold involved and that the more apps and data stored on the Fusion Drive, the slower the boot time gets. But that's just guessing.

For now, I'm going to keep it this way, putting my iMac to sleep instead of shutting it down every evening. Wake-up is instantaneous and everything is super fast and responsive. One day, with enough time on my hands, I will wipe my system once again, clean install Big Sur, and install all apps from scratch, one by one. I need to prepare this thoroughly and have to record a lot of settings. There's some fifteen years of creative work stored on this machine, and it's really fine-tuned to the limit.

Hi. My old late 2014 iMac 5k has a 1 TB Fusion Drive - whereof 128 GB is SSD. Has exactly the same issues as described. So the 128GB SSD-partition is not enough.

Seems to be Big Sur not properly supporting Fusion Drives. Disappointing - although I don't expect proper fast SSD-loading speeds. Just something like on previous generations of MacOS.

Cheers,

T

Marathonianbull,

Had you read the Terms of Use that you agreed to you would know Apple is simply our host. They do not read or participate in user to user forums. The issue is not with Mac OS, frequently the cause is what users install on their systems.

Post an EtreCheck report of your system and someone will evaluate it so we can see where that issue may be.

For the "more speed" with an external SSD, you can get read/write speeds of around 420-500 MB/s.

You do not have to do this. This is just for people who need the extra performance of an SSD.

The reason I suggested starting a new form is then we can gather an EtreCheck report from your Mac, see your exact performance numbers, and start troubleshooting yours. (Perhaps a piece of software adds to your slowdowns, etc. All cases are different.)

Cheers,

Jack

I just upgraded to macOS version 11.3 and after logging in I got a brand new notification “Optimising your Mac”. It’s stuck on there for at least 5 minutes so I assume macOS is rearranging my fusion drive! Sounds like we might have a solution!