RESOLVED - Startup drive in iMac not showing in System Preferences > Startup Disk

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Today I swapped out the conventional hard drives in both of my old iMacs, replacing them with SSD's but to have a bit of fun (well actually to put the cosmetically better one in the lounge) I swapped the drives between the machines ... so iMac A got the cloned SSD from iMac B and vice versa, quite an interesting excursion into the innards of an iMac and the dust and debris of many years was removed :)
One iMac had the 'official' OWC cable fitted to the SSD to remove the thermal cable/racing fans issue and the other had a software solution, so all fans have been reined in and both startup and read/write times have been greatly improved as a result of the SSD's.
However I have a mystery with one of the iMacs ... everything works fine, boots up great, all applications there and working, BUT when I go to System Preferences > Startup Disk not disks are displayed!
'About this mac' shows it in 'Storage' and it's there in Disk Utility ... but nothing in System Preferences > Startup Disk.
A mystery to me, any of you mac gurus out there throw any light? :)
 
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Robert
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With the problematic mac, assuming you have a wired keyboard, reboot and immediately hold down the option or alt key.

After a while a screen showing all bootable disks shows up. Select the one you want (default is Macintosh HD) follow the prompts to carry on booting.

Check >settings > Startup Disk again.
 
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gramps
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37,099
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With the problematic mac, assuming you have a wired keyboard, reboot and immediately hold down the option or alt key.

After a while a screen showing all bootable disks shows up. Select the one you want (default is Macintosh HD) follow the prompts to carry on booting.

Check >settings > Startup Disk again.
Thanks for your help Robert.
I have done that several times with no effect on System Preferences > Startup Disk ... I also did the option to force it use the SSD at Startup (which it now does without delay) but still it does not appear.
I've just added an external USB drive for Time Machine and it sees that too but System Preferences > Startup Disk remains empty! :thinking:
 
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Paul
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I assume you have taped the PRAM a couple of times, if you have try resetting the SMC. I replaced a memory module in my Mac mini once and it would not boot, after doing the PRAM and SMC hey presto, everything was OK.
 
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gramps
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I assume you have taped the PRAM a couple of times, if you have try resetting the SMC. I replaced a memory module in my Mac mini once and it would not boot, after doing the PRAM and SMC hey presto, everything was OK.
Was hopeful there as I hadn't heard of PRAM, however 1 x SMC and 5 x PRAM's later and no change. :(
 
OP
gramps
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Well long story short, 'diskutil list' showed that the drive had not been formatted to GUID either by 'Erase' or 'Super-Duper' (cloning software).
Disk Uitility > Erase didn't give the option to format as GUID but using its top menu and choosing 'Show all devices' it gave an option to Erase the native drive and included the option to formaat as GUID. Having done that and used 'Super-Duper' again to clone the original drive it is all up and working and the new SSD is visible in System Preferences > Startup Drive.
Every day a school day :)
 
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