What is the proper procedure to backup to multiple external hard drives if one wishes to rotate drives such that you may store one in a fire safe?

How about two different backup methods:

1. keep your TM disk attached for continuous backups.

2. Get another external drive, format it properly, partition it if so desired, and with the help of either SuperDuper or CarbonCopyCloner, create a full bootable clone on it from your entire system once a month. You can eject the drive when done, store it wherever, bring it back, plug it in, and tell it to update the clone.

Since TM is not bootable in and of itself (you need to use recovery to reinstall the OS/restore with TM), having a bootable clone makes it very easy to recover from a disaster.

Mount both disks and give them unique names. I call mine oddTM and evenTM because OddTM is connected on the 1st and 3rd week of the month while EvenTM is connected on the 2nd and 4th weeks. Select each as a TimeMachine drive using TimeMachine preferences and keep both connected until the first backup has completed. Or you may let one backup and unmount it then remount the second. TimeMachine is happy to work while both are mounted or just one. After about 10 days if one hasn’t been mounted you’ll get a message to that effect. That’s it. TimeMachine is smart and takes all the hard work out of it.

As an FYI:

Since a while back Time Machine creates a hidden copy of the Recovery HD, so it is possible to boot from the Time Machine backup drive in an emergency and do a full restore.

I admit I may not be up to date since I refuse to use it, but do need/want to keep up with whatever new development there is - and I've not read/heard anything that TM is bootable.

So why are you still booting into/winding up with the same recovery screen ("Utilities") as if you had used the Command + R?

Or are you telling me that you can simply choose the TM backup as a startup disk? And, is it as reliable as a tested clone?

No, it just boots the Recovery HD, so you get the Utilities Menu. But you can start it if needed just using OPTION boot and selecting the Time Machine disk icon.

I don't use Time Machine myself because I prefer having separate backup clones from which to boot, but for those using Time Machine who find themselves unable to boot from their normal Recovery HD or need to boot from a separate disk drive, it's a convenience. This started with 10.7.3, so now there isn't really much chatter about it. Sort of, "You just had to be there." 😁

One side note - the TM drive must be mounted when you install the OS for this feature. That’s how the OS recovery partition is installed on the TM drive.

I also use CarbonCopyCloner for making a clone backup but until recently TimeMachine was less obtrusive about regular backups and I have, on occasion, been very glad my computer was backed up just an hour ago. The archive feature of CCC is great when it comes to retrieve old document files but I don’t know how I’d use CCC to restore to a complete computer state 4 hours in the past which is something TM makes seamless. That’s not a feature I’ve personally used but it is a feature I’ve used on the job.

Technically, that would be the case when you begin using Time Machine. It must also be mounted in order to boot from it. As for CCC, if you archive changed files when performing an incremental backup, then you could just restore the changed files at that past point in time. It won't work, however, if you changed OS X version.

If you turn on Safety Net CCC caches all changes onto the backup drive as space permits. So, I suppose, if the backup drive maintains adequate free space for the cache then it is acting a bit like Time Machine. Or you do what many good back-uppers do: have multiple time backups. Today, past week, and past month, for example.

Time Machine is only seamless when you go looking for the old backup and find it. Not so good when they disappear for some unknown reason or you run out of space on the backup drive. I find Time Machine far more complex than CCC. Of course partly because Apple makes Time Machine appear to be a no-brainer when it's anything but.

i think we've talked backup strategies before and my motto is there's never too many and the more variety the better Which is why I use TM and CCC. What I've found professionally is that TM is a great "gateway backup" In that people who would never backup before do now. Having gotten them used to the idea I can then broaden their thinking to encompass other strategies.

I don't disagree given that newcomers to the Mac find it easy to get started. But I don't prefer it at all. I use only two backup tools: CCC and Disk Utility. I have and continue to recommend a number of other tools I have found to be pretty reliable including SuperDuper!. My once favorite tool I gave up because it became too expensive to use. Next in line from that one no longer works with Mavericks and later. I'm not a big fan of the CCC GUI, but it does work OK.

just make sure TM isn't in the process of backing up. then eject the drive. No need to turn off TM or anything. When you plug the drive in later TM will recognize it and proceed to back up to it again.

No, it just boots the Recovery HD, so you get the Utilities Menu. But you can start it if needed just using OPTION boot and selecting the Time Machine disk icon.

Thanks Kappy - so, it's just a different way to get to or boot into recovery instead of hitting Command + R; this explains a back and forth conversation I had a couple of days ago with Oglethorpe and it also explains why some people think it is bootable which, technically, it is not in and of itself (unless I've misunderstood something).

I shall now go back to my preferred bootable clone corner. Thanks for the info! I also use CCC - I appreciate knowing that I can test it and know that it will work; I have two working clones of every OS version I've got (plus what I call a "factory fresh" clone made immediately after I got the device which does not get updated purposely - I intend to use it if/when I sell the machine).

Time Machine supports multiple backup drives including network area storage volumes (NAS) as well as physically-connected external backup drives.

In , System Preferences, Time Machine, add the second drive by clicking Select Disk.

All available connected drives including connected network drives are displayed.

Select the additional drives, one at a time.

Connected Network drives are displayed on the desktop only when actively being used by Time Machine for backup.

When prompted, select 'use both' when adding the second drive.

Then choose Select or Remove at the bottom of the list of available devices and network volumes to add additional drives.

Time Machine then automatically rotates backups among the available designated devices and volumes.

If the drive is physically not present, Time Machine skips to the next available backup drive.

To DISMOUNT a drive to take it off-site, it is NOT necessary to remove it from the Time Machine preferences.

When the drive is NOT in use, dismount it by Command+clicking that Drive icon on your desktop (or in Finder) and then "Eject".

That's it.

After 10 days with no backups to a given device, Time Machine does display a message and (as I recall) asks if you want to remove that drive from the rotation.

You can never be too rich or have too many backups!