Installation of Big Sur on this 2019 iMac 21.5" has not gone well. I did not
do a clean install which was probably a mistake. Startup is slow, application
launch is slow and Mail sometimes hangs at launch. I read on the Web that Big
Sur does not get on well with fusion drives but that seems to apply mainly to
older iMacs with smaller SSDs.

EtreCheck tells me (doesn't mean much to me but might to you knowledgeable
ones):

Diagnostics Information (past 7-30 days):
2021-04-29 17:15:27 MTLCompilerService - Crash (19 times)
Executable:
/System/Library/Frameworks/Metal.framework/Versions/A/XPCServices/MTLCompiler
Service.xpc/
Contents/MacOS/MTLCompilerService Details:
dyld3 mode
2021-04-29 16:06:22 signpost_reporter - High CPU Use (2 times) Executable:
/usr/libexec/signpost_reporter
2021-04-29 08:23:34 mdsync - High CPU Use (2 times)
Executable:
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/Metad
ata.framewor
k/Versions/A/Support/mdsync
2021-04-29 08:21:03 Mail.app - Hang Executable: /System/Applications/Mail.app
2021-04-25 17:00:12 com.apple.WebKit.WebContent - Crash (2 times)
Executable:
/System/Library/Frameworks/WebKit.framework/Versions/A/XPCServices/com.apple.
WebKit.WebC
ontent.xpc/Contents/MacOS/com.apple.WebKit.WebContent Details:
dyld3 mode
Bundle controller class: BrowserBundleController
2021-04-25 12:56:31 Spark.app - Crash Executable: /Applications/Spark.app
Details:
*** Terminating app due to uncaught exception 'NSInvalidArgumentExcept ion',
reason: '-[NSNull processIdentifier]: unrecognized selector sent
to instance 0x7fff801bc610'
abort() called
terminating with uncaught exception of type NSException

I am tempted to revert to Catalina. Snag is that I don't have a Time Machine
Catalina backup as I reformatted the Time Machine drive. But I might try a
clean installation of Big Sur if someone here tells me that they have Big Sur
running satisfactorily with a fusion drive.

Much ta.

--
mhphillips at gmail dot com

On 30/04/2021 07:44, Michael Phillips wrote:
> Installation of Big Sur on this 2019 iMac 21.5" has not gone well. I did not
> do a clean install which was probably a mistake. Startup is slow, application
> launch is slow and Mail sometimes hangs at launch. I read on the Web that Big
> Sur does not get on well with fusion drives but that seems to apply mainly to
> older iMacs with smaller SSDs.
>
> EtreCheck tells me (doesn't mean much to me but might to you knowledgeable
> ones):
>
> Diagnostics Information (past 7-30 days):
> 2021-04-29 17:15:27 MTLCompilerService - Crash (19 times)
> Executable:
> /System/Library/Frameworks/Metal.framework/Versions/A/XPCServices/MTLCompiler
> Service.xpc/
> Contents/MacOS/MTLCompilerService Details:
> dyld3 mode
> 2021-04-29 16:06:22 signpost_reporter - High CPU Use (2 times) Executable:
> /usr/libexec/signpost_reporter
> 2021-04-29 08:23:34 mdsync - High CPU Use (2 times)
> Executable:
> /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/Metad
> ata.framewor
> k/Versions/A/Support/mdsync
> 2021-04-29 08:21:03 Mail.app - Hang Executable: /System/Applications/Mail.app
> 2021-04-25 17:00:12 com.apple.WebKit.WebContent - Crash (2 times)
> Executable:
> /System/Library/Frameworks/WebKit.framework/Versions/A/XPCServices/com.apple.
> WebKit.WebC
> ontent.xpc/Contents/MacOS/com.apple.WebKit.WebContent Details:
> dyld3 mode
> Bundle controller class: BrowserBundleController
> 2021-04-25 12:56:31 Spark.app - Crash Executable: /Applications/Spark.app
> Details:
> *** Terminating app due to uncaught exception 'NSInvalidArgumentExcept ion',
> reason: '-[NSNull processIdentifier]: unrecognized selector sent
> to instance 0x7fff801bc610'
> abort() called
> terminating with uncaught exception of type NSException
>
> I am tempted to revert to Catalina. Snag is that I don't have a Time Machine
> Catalina backup as I reformatted the Time Machine drive. But I might try a
> clean installation of Big Sur if someone here tells me that they have Big Sur
> running satisfactorily with a fusion drive.
>
> Much ta.
>

Hi Michael :-)

My 27in iMac has a fusion drive and is running just fine with macOS Big
Sur Version 11.3.

Did you use the updated version of EtreCheck https://www.etrecheck.com
It's no longer available in MY Apple App store. Just a 'maybe' - could
IT be causing the problems you have?!!

From what you have told us, I do not believe you will ever be able to
revert to an earlier operating system. :-(

To reinstall, from being in a shut down state, hold down the 'command'
and 'R' keys when you switch on your machine.

Good luck! :-)

--
David

David Brooks <David@nomail.afraid.org> wrote:
> On 30/04/2021 07:44, Michael Phillips wrote:
>> Installation of Big Sur on this 2019 iMac 21.5" has not gone well. I did not
>> do a clean install which was probably a mistake. Startup is slow, application
>> launch is slow and Mail sometimes hangs at launch. I read on the Web that Big
>> Sur does not get on well with fusion drives but that seems to apply mainly to
>> older iMacs with smaller SSDs.
>>
>> EtreCheck tells me (doesn't mean much to me but might to you knowledgeable
>> ones):
>>
>> Diagnostics Information (past 7-30 days):
>> 2021-04-29 17:15:27 MTLCompilerService - Crash (19 times)
>> Executable:
>> /System/Library/Frameworks/Metal.framework/Versions/A/XPCServices/MTLCompiler
>> Service.xpc/
>> Contents/MacOS/MTLCompilerService Details:
>> dyld3 mode
>> 2021-04-29 16:06:22 signpost_reporter - High CPU Use (2 times) Executable:
>> /usr/libexec/signpost_reporter
>> 2021-04-29 08:23:34 mdsync - High CPU Use (2 times)
>> Executable:
>> /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/Metad
>> ata.framewor
>> k/Versions/A/Support/mdsync
>> 2021-04-29 08:21:03 Mail.app - Hang Executable: /System/Applications/Mail.app
>> 2021-04-25 17:00:12 com.apple.WebKit.WebContent - Crash (2 times)
>> Executable:
>> /System/Library/Frameworks/WebKit.framework/Versions/A/XPCServices/com.apple.
>> WebKit.WebC
>> ontent.xpc/Contents/MacOS/com.apple.WebKit.WebContent Details:
>> dyld3 mode
>> Bundle controller class: BrowserBundleController
>> 2021-04-25 12:56:31 Spark.app - Crash Executable: /Applications/Spark.app
>> Details:
>> *** Terminating app due to uncaught exception 'NSInvalidArgumentExcept ion',
>> reason: '-[NSNull processIdentifier]: unrecognized selector sent
>> to instance 0x7fff801bc610'
>> abort() called
>> terminating with uncaught exception of type NSException
>>
>> I am tempted to revert to Catalina. Snag is that I don't have a Time Machine
>> Catalina backup as I reformatted the Time Machine drive. But I might try a
>> clean installation of Big Sur if someone here tells me that they have Big Sur
>> running satisfactorily with a fusion drive.
>>
>> Much ta.
>>
>
>
> Hi Michael :-)
>
> My 27in iMac has a fusion drive and is running just fine with macOS Big
> Sur Version 11.3.
>
> Did you use the updated version of EtreCheck https://www.etrecheck.com
> It's no longer available in MY Apple App store. Just a 'maybe' - could
> IT be causing the problems you have?!!
>
> From what you have told us, I do not believe you will ever be able to
> revert to an earlier operating system. :-(
>
> To reinstall, from being in a shut down state, hold down the 'command'
> and 'R' keys when you switch on your machine.
>
> Good luck! :-)
>

Big Sur runs well on my 2017 iMac with a Fusion drive.

Was running into some slowdowns but I think Typinator was the culprit. My
text “snippets” were large and I have a lot of shortcuts.

--
Personal attacks from those who troll show their own insecurity. They
cannot use reason to show the message to be wrong so they try to feel
somehow superior by attacking the messenger.

They cling to their attacks and ignore the message time and time again.

On 30/04/2021 18:25, Snit wrote:
> David Brooks <David@nomail.afraid.org> wrote:
>> On 30/04/2021 07:44, Michael Phillips wrote:
>>> Installation of Big Sur on this 2019 iMac 21.5" has not gone well. I did not
>>> do a clean install which was probably a mistake. Startup is slow, application
>>> launch is slow and Mail sometimes hangs at launch. I read on the Web that Big
>>> Sur does not get on well with fusion drives but that seems to apply mainly to
>>> older iMacs with smaller SSDs.
>>>
>>> EtreCheck tells me (doesn't mean much to me but might to you knowledgeable
>>> ones):
>>>
>>> Diagnostics Information (past 7-30 days):
>>> 2021-04-29 17:15:27 MTLCompilerService - Crash (19 times)
>>> Executable:
>>> /System/Library/Frameworks/Metal.framework/Versions/A/XPCServices/MTLCompiler
>>> Service.xpc/
>>> Contents/MacOS/MTLCompilerService Details:
>>> dyld3 mode
>>> 2021-04-29 16:06:22 signpost_reporter - High CPU Use (2 times) Executable:
>>> /usr/libexec/signpost_reporter
>>> 2021-04-29 08:23:34 mdsync - High CPU Use (2 times)
>>> Executable:
>>> /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/Metad
>>> ata.framewor
>>> k/Versions/A/Support/mdsync
>>> 2021-04-29 08:21:03 Mail.app - Hang Executable: /System/Applications/Mail.app
>>> 2021-04-25 17:00:12 com.apple.WebKit.WebContent - Crash (2 times)
>>> Executable:
>>> /System/Library/Frameworks/WebKit.framework/Versions/A/XPCServices/com.apple.
>>> WebKit.WebC
>>> ontent.xpc/Contents/MacOS/com.apple.WebKit.WebContent Details:
>>> dyld3 mode
>>> Bundle controller class: BrowserBundleController
>>> 2021-04-25 12:56:31 Spark.app - Crash Executable: /Applications/Spark.app
>>> Details:
>>> *** Terminating app due to uncaught exception 'NSInvalidArgumentExcept ion',
>>> reason: '-[NSNull processIdentifier]: unrecognized selector sent
>>> to instance 0x7fff801bc610'
>>> abort() called
>>> terminating with uncaught exception of type NSException
>>>
>>> I am tempted to revert to Catalina. Snag is that I don't have a Time Machine
>>> Catalina backup as I reformatted the Time Machine drive. But I might try a
>>> clean installation of Big Sur if someone here tells me that they have Big Sur
>>> running satisfactorily with a fusion drive.
>>>
>>> Much ta.
>>>
>>
>>
>> Hi Michael :-)
>>
>> My 27in iMac has a fusion drive and is running just fine with macOS Big
>> Sur Version 11.3.
>>
>> Did you use the updated version of EtreCheck https://www.etrecheck.com
>> It's no longer available in MY Apple App store. Just a 'maybe' - could
>> IT be causing the problems you have?!!
>>
>> From what you have told us, I do not believe you will ever be able to
>> revert to an earlier operating system. :-(
>>
>> To reinstall, from being in a shut down state, hold down the 'command'
>> and 'R' keys when you switch on your machine.
>>
>> Good luck! :-)
>>
>
> Big Sur runs well on my 2017 iMac with a Fusion drive.
>
> Was running into some slowdowns but I think Typinator was the culprit. My
> text “snippets” were large and I have a lot of shortcuts.

That's good to know. 😃

Did you have any problems loading macOS Big Sur Version 11.3 ?

I'm wondering how the OP has fared!

--
Kind regards,
David

On 30 Apr 2021 at 08:44:12 BST, "Michael Phillips"
<me@odtaa.com.invalid> wrote:

> Installation of Big Sur on this 2019 iMac 21.5" has not gone well. I did not
> do a clean install which was probably a mistake. Startup is slow, application
> launch is slow and Mail sometimes hangs at launch. I read on the Web that Big
> Sur does not get on well with fusion drives but that seems to apply mainly to
> older iMacs with smaller SSDs.

I'm not using fusion here but I know two people who've installed Big Sur
on their Fusion iMacs and had no trouble at all (except one with
Bootcamp, which completely refused to be useful). So it's not an
intrinsic flaw.

Update your clone/Time Machine backup, then do a clean reinstall from
Recovery and re-import your stuff. Takes a couple of hours but is way
quicker than fannying about trying to fix stuff when you don't know why
it's misbehaving.

In my younger years I'd have done the investigation. It's just not worth
the effort to me now.

Cheers - Jaimie
--
'It's one of those irregular verbs, isn't it? `I protect the
lives and property of my citizens; you keep the public
safe from an unreasonable and trouble-generating
minority; he maintains a totalitarian regime of
thought control.' -- Bernard, Yes Minister

On 30/04/2021 19:57, Jaimie Vandenbergh wrote:
> On 30 Apr 2021 at 08:44:12 BST, "Michael Phillips"
> <me@odtaa.com.invalid> wrote:
>
>> Installation of Big Sur on this 2019 iMac 21.5" has not gone well. I did not
>> do a clean install which was probably a mistake. Startup is slow, application
>> launch is slow and Mail sometimes hangs at launch. I read on the Web that Big
>> Sur does not get on well with fusion drives but that seems to apply mainly to
>> older iMacs with smaller SSDs.
>
> I'm not using fusion here but I know two people who've installed Big Sur
> on their Fusion iMacs and had no trouble at all (except one with
> Bootcamp, which completely refused to be useful). So it's not an
> intrinsic flaw.
>
> Update your clone/Time Machine backup, then do a clean reinstall from
> Recovery and re-import your stuff. Takes a couple of hours but is way
> quicker than fannying about trying to fix stuff when you don't know why
> it's misbehaving.
>
> In my younger years I'd have done the investigation. It's just not worth
> the effort to me now.
>
> Cheers - Jaimie
>

IAWTP!

On 30 Apr 2021 at 19:57:10 IST, "Jaimie Vandenbergh"
<jaimie@usually.sessile.org> wrote:

> Update your clone/Time Machine backup, then do a clean reinstall from
> Recovery and re-import your stuff.

Last night I clean installed Big Sur on an external SSD. Booting from that
it's definitely slower than Catalina.
If I do a Command-Option-Shift-R startup, won't that install Catalina?
I was happier there.

--
mhphillips at gmail dot com

On 01/05/2021 07:13, Michael Phillips wrote:
> On 30 Apr 2021 at 19:57:10 IST, "Jaimie Vandenbergh"
> <jaimie@usually.sessile.org> wrote:
>
>> Update your clone/Time Machine backup, then do a clean reinstall from
>> Recovery and re-import your stuff.
>
> Last night I clean installed Big Sur on an external SSD. Booting from that
> it's definitely slower than Catalina.
> If I do a Command-Option-Shift-R startup, won't that install Catalina?
> I was happier there.

As I mentioned yesterday, my understanding is that you /cannot/ go back.

Why not install the operating system on the hard drive of your computer?

There's nothing to lose and it doesn't take long!

Good luck!

Michael Phillips <me@odtaa.com.invalid> wrote:
> On 30 Apr 2021 at 19:57:10 IST, "Jaimie Vandenbergh"
> <jaimie@usually.sessile.org> wrote:
>
>> Update your clone/Time Machine backup, then do a clean reinstall from
>> Recovery and re-import your stuff.
>
> Last night I clean installed Big Sur on an external SSD. Booting from that
> it's definitely slower than Catalina.
> If I do a Command-Option-Shift-R startup, won't that install Catalina?
> I was happier there.
>

You can download the latest Catalina installation app from the command line
or maybe App Store, created a bootable installer on a USB stick and take it
from there, e.g.

softwareupdate --fetch-full-installer --full-installer-version 10.15.6

sudo /Applications/Install\ macOS\ Big\
Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --
/Applications/Install\ macOS\ Big\ Sur.app

Boot from the stick etc. etc.

Sorry if you already know this!

--
Cheers, Alan

On 01/05/2021 07:13, Michael Phillips wrote:
> On 30 Apr 2021 at 19:57:10 IST, "Jaimie Vandenbergh"
> <jaimie@usually.sessile.org> wrote:
>
>> Update your clone/Time Machine backup, then do a clean reinstall from
>> Recovery and re-import your stuff.
>
> Last night I clean installed Big Sur on an external SSD. Booting from that
> it's definitely slower than Catalina.
> If I do a Command-Option-Shift-R startup, won't that install Catalina?
> I was happier there.

Hi Michael

This article may help you - it's taken me a while to find it!

https://eclecticlight.co/2020/11/10/big-sur-read-this-before-upgrading/

HTH

--
David

On 01/05/2021 08:44, Alan B wrote:
> Michael Phillips <me@odtaa.com.invalid> wrote:
>> On 30 Apr 2021 at 19:57:10 IST, "Jaimie Vandenbergh"
>> <jaimie@usually.sessile.org> wrote:
>>
>>> Update your clone/Time Machine backup, then do a clean reinstall from
>>> Recovery and re-import your stuff.
>>
>> Last night I clean installed Big Sur on an external SSD. Booting from that
>> it's definitely slower than Catalina.
>> If I do a Command-Option-Shift-R startup, won't that install Catalina?
>> I was happier there.
>>
>
> You can download the latest Catalina installation app from the command line
> or maybe App Store, created a bootable installer on a USB stick and take it
> from there, e.g.
>
> softwareupdate --fetch-full-installer --full-installer-version 10.15.6
>
> sudo /Applications/Install\ macOS\ Big\
> Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --
> /Applications/Install\ macOS\ Big\ Sur.app
>
> Boot from the stick etc. etc.
>
> Sorry if you already know this!

Are you SURE that will install Catalina?

Alan B <alanrichardbarker@nospamgmail.com.here> wrote:
> Michael Phillips <me@odtaa.com.invalid> wrote:
>> On 30 Apr 2021 at 19:57:10 IST, "Jaimie Vandenbergh"
>> <jaimie@usually.sessile.org> wrote:
>>
>>> Update your clone/Time Machine backup, then do a clean reinstall from
>>> Recovery and re-import your stuff.
>>
>> Last night I clean installed Big Sur on an external SSD. Booting from that
>> it's definitely slower than Catalina.
>> If I do a Command-Option-Shift-R startup, won't that install Catalina?
>> I was happier there.
>>
>
> You can download the latest Catalina installation app from the command line
> or maybe App Store, created a bootable installer on a USB stick and take it
> from there, e.g.
>
> softwareupdate --fetch-full-installer --full-installer-version 10.15.6
>
> sudo /Applications/Install\ macOS\ Big\
> Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --
> /Applications/Install\ macOS\ Big\ Sur.app
>
> Boot from the stick etc. etc.
>
> Sorry if you already know this!
>

Given that you will undoubtedly have to erase your iMac’s hard drive,
hopefully you’ll have a TM backup to migrate back your personal stuff!

--
Cheers, Alan

On 1 May 2021 at 08:44:25 IST, "Alan B"
<alanrichardbarker@nospamgmail.com.here> wrote:

> You can download the latest Catalina installation app from the command line
> or maybe App Store, created a bootable installer on a USB stick and take it
> from there, e.g.

I found a link that brings me to the download Catalina page on the App Store.

Do I really need a bootable installer? Can I not launch it from the Big Sur
external SSD and let it do its stuff on the erased internal hard drive?

--
mhphillips at gmail dot com

On 1 May 2021 at 09:30:45 IST, "Alan B"
<alanrichardbarker@nospamgmail.com.here> wrote:

> Given that you will undoubtedly have to erase your iMac’s hard drive,
> hopefully you’ll have a TM backup to migrate back your personal stuff!

I do have a TM backup but it's APSF formatted. I'm not sure if Catalina's
Migration Assistant will read from that. I suppose I can drag and drop the
Home Library folder contents and re-install applications afresh.

--
mhphillips at gmail dot com

Michael Phillips <me@odtaa.com.invalid> wrote:
> On 1 May 2021 at 08:44:25 IST, "Alan B"
> <alanrichardbarker@nospamgmail.com.here> wrote:
>
>> You can download the latest Catalina installation app from the command line
>> or maybe App Store, created a bootable installer on a USB stick and take it
>> from there, e.g.
>
> I found a link that brings me to the download Catalina page on the App Store.
>
> Do I really need a bootable installer? Can I not launch it from the Big Sur
> external SSD and let it do its stuff on the erased internal hard drive?
>

Judging by my recent experience with installing macOS to my CCC backup
drive, then tentatively yes, although the app was on my internal drive of
course.

--
Cheers, Alan

Michael Phillips <me@odtaa.com.invalid> wrote:
> On 1 May 2021 at 09:30:45 IST, "Alan B"
> <alanrichardbarker@nospamgmail.com.here> wrote:
>
>> Given that you will undoubtedly have to erase your iMac’s hard drive,
>> hopefully you’ll have a TM backup to migrate back your personal stuff!
>
> I do have a TM backup but it's APSF formatted. I'm not sure if Catalina's
> Migration Assistant will read from that. I suppose I can drag and drop the
> Home Library folder contents and re-install applications afresh.
>

Without doing some research I’m not sure. I used a fresh TM drive when I
upgraded to Big Sur thus leaving my HFS+ TM drive intact just in case I
needed to go back to Catalina. But as you say the bottom line is that you
can reinstall apps and copy over at least your ~/Documents folder. I
suspect you would need to be careful what you copied over from -/Library.

--
Cheers, Alan

On 1 May 2021 at 08:13:17 IST, I wrote:

> If I do a Command-Option-Shift-R startup, won't that install Catalina?

No, it installs Mojave!

--
mhphillips at gmail dot com

Michael Phillips <me@odtaa.com.invalid> wrote:
> On 1 May 2021 at 08:13:17 IST, I wrote:
>
>> If I do a Command-Option-Shift-R startup, won't that install Catalina?
>
> No, it installs Mojave!
>

Was that the OS it came with?

--
Cheers, Alan

Alan B <alanrichardbarker@nospamgmail.com.here> wrote:
> Michael Phillips <me@odtaa.com.invalid> wrote:
>> On 1 May 2021 at 08:13:17 IST, I wrote:
>>
>>> If I do a Command-Option-Shift-R startup, won't that install Catalina?
>>
>> No, it installs Mojave!
>>
>
> Was that the OS it came with?
>

Looks like you need to install via the Catalina installer app as discussed
previously. You’ll probably get offered a BIg Sur upgrade if you just leave
it!

--
Cheers, Alan

Alan B <alanrichardbarker@nospamgmail.com.here> wrote:
> Alan B <alanrichardbarker@nospamgmail.com.here> wrote:
>> Michael Phillips <me@odtaa.com.invalid> wrote:
>>> On 1 May 2021 at 08:13:17 IST, I wrote:
>>>
>>>> If I do a Command-Option-Shift-R startup, won't that install Catalina?
>>>
>>> No, it installs Mojave!
>>>
>>
>> Was that the OS it came with?
>>
>
> Looks like you need to install via the Catalina installer app as discussed
> previously. You’ll probably get offered a BIg Sur upgrade if you just leave
> it!
>

Actually thinking about it, if you have done a clean install I’d be tempted
to allow Software Update to upgrade the OS to Big Sur and then reimport
from your now compatible APFS formatted TM drive as Jamie suggested. I
can’t see why Big Sur should be running so badly on your iMac compared to
Catalina. Reinstalling both the OS and your data might well clear the
glitch that was causing the iMac to perform so badly. If the problem
persists only then consider a Catalina reinstall.

--
Cheers, Alan

On 1 May 2021 at 19:46:12 IST, "Alan B"
<alanrichardbarker@nospamgmail.com.here> wrote:

> Michael Phillips <me@odtaa.com.invalid> wrote:
>> On 1 May 2021 at 08:13:17 IST, I wrote:
>>
>>> If I do a Command-Option-Shift-R startup, won't that install Catalina?
>>
>> No, it installs Mojave!
>>
>
> Was that the OS it came with?

Must be.

--
mhphillips at gmail dot com

On 1 May 2021 at 19:49:44 IST, "Alan B"
<alanrichardbarker@nospamgmail.com.here> wrote:

> Looks like you need to install via the Catalina installer app as discussed
> previously. You’ll probably get offered a BIg Sur upgrade if you just leave
> it!

Having downloaded the Catalina installer I now find that it won't run from Big
Sur, so I'll have to create a bootable installer drive. Bugger.

--
mhphillips at gmail dot com

On 1 May 2021 at 20:13:37 IST, "Alan B"
<alanrichardbarker@nospamgmail.com.here> wrote:

> Actually thinking about it, if you have done a clean install I’d be tempted
> to allow Software Update to upgrade the OS to Big Sur and then reimport
> from your now compatible APFS formatted TM drive as Jamie suggested. I
> can’t see why Big Sur should be running so badly on your iMac compared to
> Catalina. Reinstalling both the OS and your data might well clear the
> glitch that was causing the iMac to perform so badly. If the problem
> persists only then consider a Catalina reinstall.

I'm coming reluctantly to the same conclusion.

--
mhphillips at gmail dot com

On 02/05/2021 07:50, Michael Phillips wrote:
> On 1 May 2021 at 20:13:37 IST, "Alan B"
> <alanrichardbarker@nospamgmail.com.here> wrote:
>
>> Actually thinking about it, if you have done a clean install I’d be tempted
>> to allow Software Update to upgrade the OS to Big Sur and then reimport
>> from your now compatible APFS formatted TM drive as Jamie suggested. I
>> can’t see why Big Sur should be running so badly on your iMac compared to
>> Catalina. Reinstalling both the OS and your data might well clear the
>> glitch that was causing the iMac to perform so badly. If the problem
>> persists only then consider a Catalina reinstall.
>
> I'm coming reluctantly to the same conclusion.
>

WHY DIDN'T YOU LISTEN TO ME?!!!

Michael Phillips <me@odtaa.com.invalid> wrote:
> On 1 May 2021 at 20:13:37 IST, "Alan B"
> <alanrichardbarker@nospamgmail.com.here> wrote:
>
>> Actually thinking about it, if you have done a clean install I’d be tempted
>> to allow Software Update to upgrade the OS to Big Sur and then reimport
>> from your now compatible APFS formatted TM drive as Jamie suggested. I
>> can’t see why Big Sur should be running so badly on your iMac compared to
>> Catalina. Reinstalling both the OS and your data might well clear the
>> glitch that was causing the iMac to perform so badly. If the problem
>> persists only then consider a Catalina reinstall.
>
> I'm coming reluctantly to the same conclusion.
>

At least you’ve proved it IS possible to downgrade from Big Sur ;-)

--
Cheers, Alan