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I have two external drives for backup - one has Time Machine and the other has my Super Duper clone. The likelihood of the clone drive ever getting full is very slim, but the TM drive could.

I understand I can ask TM to continue recording on a second drive rather than delete files from the drive it first resided on. In my case, it would be continuing on the drive that has the SD Clone. There is plenty of room for both.

Will either Time Machine or Super Duper care? If they don't, I won't worry. Otherwise, am I better off to go back to scratch and partition the clone drive?

ryck

You can have Time Machine back up to a different volume at any time. This starts a new historical archive if the new volume has never been used for backup from this machine. The new backup and the old backup are completely independent. No history is copied over from the old backup to the new one.

If you switch back to the original volume, TM will just pick up where it left off on that volume, as if you had simply left TM turned off all that time.

This is a great way to keep offsite backups. I use TM format for my offsite backups which, by their nature, do not need to be up-to-the-hour like regular backups. Once a week, I mount one of my offsite backups and tell TM to back up to it; it copies over everything that changed since the last time I used that disk. Then I switch TM back to my regular volume and let it resume its hourly schedule. The disk that I just backed up to is taken offsite and swapped with the alternate offsite disk, which I bring home. Once home, I again tell TM to do one backup to it, and then go back to the normal disk. This way, each of my offsite disks gets approximately weekly backups, and at all times at least one of them really is offsite. Recovering from a TM backup is as fast as recovering from a SuperDuper backup. (Note: I said recovering from, not booting from. The TM backup is, of course, not bootable. On the other hand, if I need the offsite backups, I probably also had to buy a new computer, and the extra time to recover my data is not the main concern.) The main advantage of using TM format is that it gives me more recovery options and more history.

If you tell TM to back up to the same disk (whether to the same or a different partition) as your SD backup, you have only one backup. You're only fooling yourself if you think using two pieces of software somehow turns one physical disk into two. If the disk dies, you lose everything on it, no matter how many copies you had on the disk.

With that caveat, TM and SD will not interfere with each other, at least not until you run out of room. SD will notice the TM backup and work around it, but if you run of space SD has no way to ask TM to free up old backups, and the SD backup will fail.

If a TM volume fills up, and it starts deleting old backups, there's probably no need for concern. Ask yourself if the backups being deleted are really still relevant. Chances are, they aren't. Remember that if TM throws away a two-year-old backup, you aren't losing what you had two years ago. You're losing only what you had already trashed two years ago.

If you decide you want to keep the old TM history, but on a larger disk, there are two ways to copy the old backup archive over: SD knows how to clone a TM disk without disturbing any of TM's metadata; or if you're on Snow Leopard just drag the Backups.backupdb folder across, and Finder will do the right thing. Either way, you only need to tell TM to start backing up to the new disk, and it will pick up right where it left off, as if it had been backing up to that disk all along.

Thanks for all the info...it's appreciated.


Actually, I knew that but I can see, from my "start from scratch" comment, how it could be understood otherwise. I just thought that, if I partitioned the drive, it might keep TM and SD from bumping into one another. However, it appears that's not much of an issue anyway.


Good point. When I thought about it, I couldn't recall any occasion when I went a long distance back in TM.

ryck