Backup of Snow Leopard wants to boot Yosemite installer

[flaubert]

Hi, here is my situation... I was a Snow Leopard holdout for a long time, through Lion / Mountain Lion / Mavericks. I finally decided when Yosemite came out to upgrade (the iOS integration was enough to get me to switch). So, I downloaded Yosemite installer, made a clone of my internal hard disk to an external drive using Super Duper, and booted from the external disk. I then wiped the internal disk, and installed Yosemite from the installer program while booted from the external disk. I don't recall having any problems doing the install; I probably had to point the installer at the internal disk at some point so as make it install there, rather than the external disk I was booted from.

So, everything is fine as far as Yosemite is concerned. I have Filevault working, etc. The problem is, I would like to be able to boot from that backup clone of Snow Leopard on the external drive from time to time. However, when I boot the computer with the external drive connected and hold down the option key to get a choice of boot drives, it shows me two drives: my internal (Yosemite) drive, and the external drive shows up as "OS X Installer." Apparently the external drive is marked in some way to boot into the Yosemite installer? How can I make it go back to booting Snow Leopard in the usual way?

By the way, I've looked at the external drive while booted into Yosemite, and all my old Snow Leopard files appear to be there.

Thank you for any advice you may have.

 

[LCPepper]

Does the Yosemite Install actually launch when you select the "Installer" from the boot selection menu?

 

[flaubert]

It starts to boot with a Yosemite-style thin grey progress bar, but after a minute or so the bar goes away, and then it displays a grey "no entry" type of symbol (circle with a diagonal bar). Nothing happens after that, so I held the power button down until it shut down. I think I have a second backup on another disk, in encrypted form; I can't boot from it directly, but I could probably clone it to this external disk, and get around this problem. I was hoping it was something simple, like "delete file XYZ and then it will boot the normal kernel."

 

[LCPepper]

It's really strange. Because to get the installer to a bootable state you'd have probably had to wipe the external drive. But seen as your date is still all there then that's not the case...

Have you tried deleting all the Yosemite related bits and bobs on there?

What also could be an issue is Apple's thing about not being able to run newer OS X versions on older hardware/ on older hardware that's had newer OS X versions installed. Which would explain the error symbol... But this can also indicate a borked installation/ backup/ drive; which might not pose a problem when browsing files, but causes issues of trying to boot.

Have you tried repairing the disk in Disk Utility?

Also, if you do have a back up that's encrypted, you could mount it and decrypt it on your current Yosemite machine and then you'd be able to boot from it.

 

[Eithanius]

Is it possible that you may have cloned SL into an external drive that contains Master Boot Record as Partition Map Scheme...?

 

[flaubert]

Is it possible that you may have cloned SL into an external drive that contains Master Boot Record as Partition Map Scheme...?

I don't think that is the case here, as I clearly remember booting to this external drive when I went to install Yosemite on the internal drive. But I appreciate your suggestion, thank you.