Wondering About A Few Things Time Machine Is Doing

Hello All!

On the excellent advice of 2 members here, I just started using Time Machine to do incremental backups of my hard disk. It's great & quite easy to set up and operate.
But, I noticed a few things I am simply curious about. I am sure they are not problems- Just curiosities.

When I run Time Machine I will open its Preferences just to watch what is going on. (Yep- I'm that bored). These questions are related to incremental backups.

Question A) Repeating
When Time Machine runs, it shows how many files and how many bytes are being backed up.
After it finishes, it immediately re-starts the process on its own, only this time it is backing up far less files.
For Example- One one incremental, it backed up 675 files at 3.6 Mb. On the re-run it backed up 150 files & 16 Kb.

I am wondering why it runs, then re-runs immediately and by itself.

Question B) Why do so many files change so very quickly?
If I run a Time Machine backup and then do not do anything else at all, I can ask Time Machine to do another backup lots of files are backed up again. I assume that these are changed in some way in a very short time.

As an example- On one backup it did 975 files and 12.3Mb. When I immediately initiated another backup, the program backed up 515 files & 2.6 Mb. They must be files that have been changed in some way.

I've tried this with the Airport on and with it off (Just in case some network action is taking place.) I looked around Activity Monitor and did not see anything crazy going on. Time Machine scheduling is set to OFF. I use it manually. I don't have any other scheduled tasks in the background. My automatic off-site backup program was also off during these tests. For that program "Off" is 'Engine Stopped".

I'm wondering what gets changed in such a short period of time, and with out any user input?

Thanks for sharing your knowledge. I always enjoy learning about how the OS works.

Paul

I don't know why it's running back to back, but the OS is constantly changing system cache and log files. The console log, for example, gets hundreds of update every minute, so TM backs it up, then when it looks for what changed, it sees new timestamps on the logs and caches, so it backs them up again. It doesn't look inside the file for just the few lines added, it backs up the entire log file, which can be very large if you haven't cleaned it out recently. (If you feel the need to clean out that sort of stuff, look for Onyx to do that. It's the one tool recommended here for the occasional cleaning. I run it about once a year, just because.)

Jake is right.
Even during a backup, files can be changed on the disc, requiring a backup.
The console log and the Time Machine database on your disc change during backups so Time Machine will back these up after the normal TM run has finished.

Cheers ... McBie

Thank You Jake and McBie
I do appreciate the information you both shared.

This morning, I had a chance to (ignore work and...) look around the Console Logs. That was an interesting trip inside OS X. Very Interesting.

It never occurred to me that the Time Machine database itself was changed during the backup and that this is the 'repeat' I see after the backup is finished.

I will carefully clean the log files once in a while with Onyx. Some of them sure seem huge. I enjoy using Onxy for the few things I use it for (so far, anyway). I force the maintenance scripts and use it for permission repairs after a repair from Disk Utility, as well as some minor cleaning of caches & stuff.

Thanks Again & Thank You for introducing me to the Console & its log files.
Paul