A "public beta" mount/unmount surprise for you.

[Michael@wengam]

As far as making the script work regardless of which disk I start up from, I am considering naming the backup disk's OSX partition with the same name as the normal startup partition. Then my login script could simply tell diskutil to unmount the OSX startup partition by name (in my case, OSX_silver). I think this should succeed in unmounting the backup partition but fail for the startup partition, shouldn't it? I already tried unmounting the startup partition, in Terminal, and it did indeed fail to unmount and seems unaffected, but I am wondering if there is any harm in doing that? I am also wondering how diskutil will react to the potentially ambiguous request: will it stop and wait for the disk choice to be be resolved?

I would try this out, but I am a bit confused about the ramifications of mounting simultaneous same-name partitions. I notice that you do sometimes recommend naming backup partitions the same as primary ones -- for example, to preserve paths and aliases. Have you written a summary note about the pros and cons -- or precautions -- of doing this anywhere?