Reverting to an earlier OS

My wife’s iMac is mid-2014 vintage. In the past few months it has become almost unusable, as if stuck in molasses. Everything takes forever to happen. I believe this is due to Big Sur being too demanding on the machine. Even after a restart trying to to update to 11.6.1 basically stalled twice. So right now I wonder what is the best course. A clean reinstall of 11.6 Big Sur, or reverting to Catalina. I have never reverted to an earlier OS version myself, so I am hesitant to embark on this. Thoughts? Advice? Step by step instructions?

Is your iMac booting from a hard drive or an SSD? That’s always where I look first when someone talks about molasses.

In general, no macOS upgrade should result in a major performance slowdown as a matter of course. It’s possible that there’s some other factor in play, but such things can usually be resolved by clean installs.

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A HD, Adam.

I’d suggest installing either Big Sur or Catalina on an external ssd. It will be a lot faster than anything you will get on your HD.

Yeah, an SSD will make a massive difference in performance. It’s the single best thing you can do. See

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I agree with the others regarding SSD but I’d also be concerned the hard disk could be failing if the decline has been noticeably quick.

An external SSD it will be then. Thanks all.

I use a Toshiba X700 external USB SSD and it makes all the difference booting up and better performance in general compared to the internal hard drives in my 2012 Mac Mini. I also use Samsung T5 and T7 models for storage and backup. Prices are lower than two years ago when I bought some of mine with increased storage capacity so you can’t go wrong.

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You didn’t say exactly which 2014 iMac she has, but the 21.5" has a Thunderbolt 1 port which could double the speed of that SSD over USB and the later 27" model has a Thunderbolt 2 port which could quadruple the SSD speed.

Okay, I finally got a Samsung T5 1 TB external ssd drive. I must use a USB A port on the computer to plug it in. There is no USB C port and the two Thunderbolt ports are the wrong kind. I think they are Thunderbolt 1 ports. I have mounted the drive, but if I want to follow the instructions given in the link Ace gave earlier, I am stuck at the first step: I can’t reformat to APFS. It’s not in the options available. The drive is presently ExFat, I can reformat it to MacOS Extended (Journaled), case sensitive or not. Will either work? Can I then use CarbonCopy to clone the internal disk (which is APFS)? Is this even worth it or am I replacing a slow poke with another slowpoke? Sorry to be so lost, I remember when macs were simple (I go back to the very first mac!). Before there were new connectors every other year.

Your inability to reformat the volume is probably because APFS isn’t just a file system that you can slip into any generic disk partition (like HFS+ and ExFAT). You may need to re-partition the disk in order to create an APFS container partition, within which you can create APFS volumes.

Also, if the partition table is not GPT, you will have to change it. I’m almost certain that APFS won’t work on a device formatted with the older MBR (used by most PCs prior to GPT) or APM (used by Macs prior to GPT). The partition table bundled with your SSD was probably MBR, since it is less than 2TB (the maximum size supported by MBR on devices with 512 byte disk blocks - the most common kind).

Assuming you can erase the entire device (make sure you have a copy of the data on some other device), the easiest way to do this is to use Disk Utility to erase the entire device, not just a single volume:

  • Launch Disk Utility

  • Select View → Show All Devices from the menu-bar, so you see the SSD itself, not just the volumes it contains.

  • Select the SSD device (not any volumes it may contain). This is critical, because you are going to end up repartitioning it as well as creating an APFS volume. The device name will typically end with the word “Media”, but I don’t know if it always will.

  • Click the Erase button. You will see a dialog asking you how you want to erase it. For example, I see this for one of my external USB hard drives:

    Screen Shot 2021-12-21 at 00.45.43

  • Provide a name for the volume you want to create. Make sure the format is APFS and the partition scheme is “GUID Partition Map” (as shown above).

  • Click Erase

That should do it.

WRT using CCC to clone your internal disk:

  • You can clone your Data volume to either an APFS or an HFS+ volume. Either should work. When restoring your system, use the Recovery partition (or Internet Recovery) to erase and reinstall macOS. Once that’s done, use Migration Assistant to move as much as possible from your backup of the Data volume to the newly-installed system.

  • If you want to make your backup bootable, the destination will need to be APFS. But bootable backups of Big Sur and later is not generally recommended, for a variety of reasons I don’t want to get into with this reply. But know that if you want to do this, the destination will need to be APFS, because modern macOS releases (definitely Big Sur, I think also Catalina) can’t boot from HFS+ volumes.

See also:


As David has already explained how to format the T5, you can use his instructions which is what I did recently with my own T5. By the way, CCC would tell you that you have to have the target disk as APFS for a bootable clone so you would have realized the necessity of that in any event. I currently use a T5 for a bootable backup for Catalina and Mojave partitions and it works fine. My first SSD was a Toshiba XS700 which is my main boot drive, one for Mojave and a later one for Catalina. When I first set it up three years ago, I immediately noticed and enjoyed the faster boot times and overall faster performances opening programs, large files etc. The internal drives in my 2012 Mac Mini are probably similar to yours and the SSD drive will improve on their speeds. Going through the USB port is not as fast as Thunderbolt, but it’s still an improvement and the tiny sizes of the drives allow them to be moved easily out of the way compared to some larger cases.

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The picture you provided finally did the trick for me. One has to pick the correct scheme FIRST. No wonder why I couldn’t find my way out of this particular paper bag! Thank you

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A HDD will probably not be fast enough to saturate a USB 3 interface. For example, my external HDD (4TB Toshiba N300), has the following relevant specs:

  • Maximum interface speed (SATA 3): 6 Gbit/s
  • Typical data transfer speed: 232 MB/s (1.8 Gbit/s)

In comparison, USB 3’s top speed is either 5 ot 10 Gbit/s, depending on which variety of USB 3 is supported by the computer and the drive’s enclosure.

While my HDD is definitely not the fastest you can get, it’s also far from the slowest. I would consider it typical of a 7200 RPM drive.

Any SSD you get should be able to saturate a USB 3 interface. A SATA device topping out at 6 Gbit/s and an NVMe device should go up to whatever the USB enclosure supports. Yes, an NVMe drive in a Thunderbolt enclosure will outperform any USB device, but either will outperform an HDD.

All of those specs are important but I was referring to my experience going from the internal drives to an external USB SSD which is an off the shelf model, not an internal one put into a case. The OP is using a T5 model off the shelf so the speeds are a lot lower than what some users have described here using internal SSD’s in external cases.

All true. The observed performance will depend on what you’re coming from.

If the existing internal drive is an HDD, then any SSD, even USB, will be significantly faster.

If the existing internal drive is a SATA SSD, then a USB SSD may be slower (if it’s a 5G USB 3.0 device), the same (if it’s a SATA SSD in a 10G USB 3.2 enclosure) or faster (if it’s an NVMe SSD in a 10G USB 3.2 enclosure).

If the internal drive is an NVMe SSD, then you can probably expect any external USB SSD to be slower, but it will be a matter of personal opinion whether the resulting system performance is acceptable or not.