Hey, look ma, no exclamation point in that title! Had to happen sometime.
So, the Safety Clone.
The Safety Clone is one of the most unique things that SuperDuper! does, but also one that is potentially misunderstood. I was really happy to see Ted Landau’s Macworld post suggesting it for Tiger, as it’s a pretty painless way of testing whether an OS upgrade works, but it’s important to understand what it is, and what it isn’t.
First off, the Safety Clone is not (not!) a “backup” in the conventional sense, so please don’t use it this way. We provide two scripts—“Backup - all files” and “Backup - user files” that are intended to be used as backups… hence their names. But the Safety Clone is something entirely different.
The idea is this: the Safety Clone isolates a copy of your system on its own partition. When you boot from it, you can install system-level updates (like Tiger) in this “Sandbox” while still retaining the ability to “roll back” to your original should something go wrong.
How do we do this?
Basically, the Safety Clone copies the “system” files that are considered to be “owned” by Apple: most of the things outside your Home folder. And, it shares those files that are “owned” by you.
For the more technically inclined, we “share” the files by symlinking them as appropriate. Details of what files are shared and what files are copied can be obtained by examining the script involved. If you have questions, ask!
So, we create two copies of your system—one in the “Sandbox”—but have only one copy of your user files, which reside on the original drive. When you boot from the Sandbox, you’re on an isolated system, but you’re changing your original user files. That way, when you boot back to your original OS, all the changes you made are there—because you changed the original files!
Just remember: it’s not a backup. It’s a checkpoint of your system that allows rollback of the OS. You must continue to back up your original volume if you want to protect against data loss. (Backing up the “Sandbox” isn’t usually necessary, since the things stored on it aren’t “personal”.)
Tips and tricks about “rolling back” in the next tedious installment!
