Cycling backups with multiple Time Capsules

backuptime-capsule

I am using Time Capsule for backing up my Mac at home and like this solution for its convenience (automatic hourly backups in the background, etc.).

I would now like to add an off-site backup to the mix, with the intention of cycling backup media between on-site (used for backup) and off-site (sitting at a safe location) every week or so. (An online backup service is not an option.)

Could I accomplish this by buying a second Time Capsule and just switching between the two (with Open Time Machine Preferences | Select Disk) to effect the cycling. Would this work and/or are there perhaps better (also cheaper) ways to do this?

(I understand that Time Capsule has been designed to be kept running, so the device could perhaps suffer from being turned off/on relatively frequently, i.e. every other week. I also understand that some NAS support hot swapping, which sounds promising, but isn't really meant to support this scenario either. Creating a RAID 1 between the Time Capsule — now to be kept on-site and one from a set of USB drives — now to be cycled — sounds elegant but is perhaps more complex than a backup solution ought to be?)

Best Answer

Time Machine supports multiple drives since Mountain Lion: that should be sufficient to support the desired backup scenario (1 Time Capsule + 2 cycled USB drives).

(Re answering own question: What can I say ... writing down a question often helps in finding the answer, and I've only recently upgraded from OS X 10.7.)

Related Solutions

Mac – Time Machine – multiple backup destinations for a “separate weekly”

Basically, I would recommend not trying to constrain time machine to only a weekly interval on the offsite drive.

That being said, you can have both drives work totally independently as that is how the software is engineered. If you really only want a weekly snapshot, only connect the weekly drive once a week and force a rotation of the destination:

 tmutil startbackup --rotation

Once you have a backup to the weekly drive, eject it and send it away. As long as all dives get reattached every 14 days or so, you won't get a warning dialog that any are out of date.

Again, you can certainly enforce a single weekly backup by the procedure you follow but two things make that practice less needed than you might expect:

The backup intervals are very low space overhead compared to the size of cheap backup disks.

On my worst Mac, the system averages 5 MB of overhead for system log files so in absence of user files changing, you have 24 daily and 31 monthly snapshots you would avoid storing 275 MB (or 0.0003 of a one TB drive) if you were on a strict one per week schedule.

Since the cleanup of old backups is so fast and the storage impact so low, most clients with offsite rotation end up just swapping disks each week and let the software cull the extra snapshots per the normal schedule, leaving weekly snapshots more than a month old.

MacBook – Time machine/capsule read-only error

Read only is a fail safe mode for the backups. It means there was a problem detected with the backup and you can only restore from it.

The system won't continue adding files since that would risk your losing even the ability to recover the files.

There is a procedure to re-attach a Mac to the existing backup once logic boards are replaced, but they assume that there isn't a failure of the backup at the same time.

You should have support from the people who replaced the logic board to help make sure you aren't just missing the steps to re-establish a backup, but if the backup were mine, I'd try backing up to a blank new USB drive and get a good backup now and then troubleshoot the Time Capsule to remedy the error causing the read-only status without risking your only backup. (Since the troubleshooting is to use Disk Utility to repair or erase the Time Capsule and then start over with an initial backup).

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