June 12th, 2008 • 3:33 pm
Following my recent misadventures with a damaged Time Capsule backup disk image causing repeated kernel panics, and some reader feedback about the issue, I downloaded a small third-party utility called TimeMachineEditor.
It is a simple application whose sole purpose is to enable you to customize the schedule of Time Machine backups.
I have reasons to suspect that the damaged disk image on the Time Capsule was caused by the fact that I abruptly interrupted a TM backup in progress by closing my wife’s laptop while the screen was asleep.
A Betalogue reader suggested via e-mail that he didn’t think that any program could handle such a situation gracefully, whether it’s Time Machine or a third-party backup utility such as Retrospect.
My response to this is that, from the user’s perspective, it’s an unacceptable limitation of the backup software. There is simply no way that the user of a Mac laptop should also be expected to always make sure that there is no TM backup in progress before closing his machine.
The whole point of having a reliable backup setup is that you don’t even have to think about it. A limitation of the system that forces you to constantly remember to double-check before you do something as simple as closing your laptop directly breaks this fundamental requirement of a good backup system.
If there are engineering limitations that make it difficult for a backup system to handle such a situation gracefully—and indeed, that can so easily cause disk image corruption and catastrophic kernel panics—then these engineering limitations need to be urgently eliminated. Engineering is at the service of usability.
That said, until Apple fixes this problem and eliminates the risk of users inadvertently damaging Time Machine disk images (with such disastrous consequences), I need to be pragmatic and find a solution.
In my view, reducing the frequency of Time Machine backups is a easy way to significantly reduce the risk of damaging the disk image. I really do think that hourly backups are overkill, especially for someone like my wife. Sadly, there is nothing in the Time Machine user interface that lets you adjust the frequency of backups.
But apparently this TimeMachineEditor application can change the backup interval by simply “updat[ing] a system configuration file.” Presumably this means that Time Machine’s internals do include options for adjusting the schedule, but that these options simply aren’t accessible to the end user through the user interface.
So I installed the utility this morning and used it to change the schedule to a single daily backup at 3:00 pm. As the TimeMachineEditor instructions indicate, the change is not reflected in the Time Machine preference pane, which still states that backups will take place hourly, and which now gives a wrong time for the next scheduled backup. But regardless of what the preference pane says, it does appear that the change works, and my wife’s laptop has only run its Time Machine backup once today, exactly at 3:00 pm.
So it looks like the utility works. I still had to explain to my wife that, in order to avoid problems with the Time Capsule in the future, from now on she should make sure that, if she needs to close the laptop around 3:00 pm, she should always make sure that no backup is in progress. But it’s much better than having to remember to check this all the time, all through the day.
It’s not an ideal solution, but it’s probably an acceptable compromise until the engineers get their act together. It certainly should greatly reduce the risk of another incident of irreparable disk image damage on the Time Capsule—at least I hope so!