ShirtPocket clone doesn't show up as a bootable volume

[Dan Lester]

I have several copies on different storage media that work fine as bootable backups. These are made with identical SD options. ONE copy, to ONE particular partition on ONE particular drive (as it turns out, a WD rotating hard drive) seems to copy successfully, but then it simply doesn't show up as a bootable volume in "Startup Disks", or when I try to do an external startup using Startup Options. I repeat the copy over and over and, same deal each time. No problem with an identical partition on the same drive. What's up with that?

[dnanian]

What macOS versions are invalid, how large is the drive, how is it formatted and how large are the partitions?

[Dan Lester]

This is on a 2021 silicon M1 iMac running Monterey 12.6.3. The drive is formatted APFS. These are two partitions out of three equal ones, each 333GB in a 1TB drive.

[dnanian]

Sounds like you need to review this post:

https://www.shirtpocket.com/blog/ind...ot_a_marathon/

[Dan Lester]

What I see there is

My Backup Isn't in Startup Disk Preferences!
Often the backup won't show up in the Startup Disk Preference pane. That's OK! As mentioned in a previous post, you should use Option+Boot (on an Intel Mac) or Power+Boot (on an Apple silicon Mac), and it should show up there.

But, as I said, the disk doesn't show up in Power+Boot either.
In Disk Utility, these partitions looks EXACTLY the same. Maybe I need to just erase the whole disk and repartition?

[dnanian]

Sorry, it wasn't clear that's what you were talking about, since you didn't say Power+Boot...you said "Startup Options".

Dan, let's move this to email - I'm going to need more information from you, and it's much easier to get it that way.