HT201250 Is Time Machine Scalable?

Question

I have a MBA with about 150GB of files and a TIme Capsule.  It looks like this is too much for Time Machine to handle.  The initial backup takes 2 days and the hourly backups take more than an hour.  While the backup processes are running my MBA occasionally becomes unresponsive for a minute at a time.  This means that if I keep automatic backups enabled it is difficult to use the computer because of all the interruptions.  When I turn off automatic backups and only manually backup files Time Machine periodically tries to perform a complete backup which takes 2 solid days.
I did some digging to see how Time Machine works.  It looks like Time Machine mounts the remote drive and performs all comparisons as a local file system operation.  This means that to check which files have changed Time Machine has to read information about every file on the remote disk across the network.  During this operation Activity Monitor shows that my wireless network is saturated--note that I have an Air which does not have an ethernet port.  This appears to limit Time Machine's/Capsule's scalability.
I have been digging around to see if I can make this purchase useful, but it does not apear that there are very many tuning options with Time Machine.  Any suggestions are welcome.  Otherwise I will have to return my Time Capsule and look for a more scalable solution.  Any recommendations for alternatives would be welcomed as well.

Answer 1

Question?  Do you have a Virtual Machine running on your Mac (VMware Fusion, Parallels, VirtualBox) with a guest OS installed?  Any changes made by a guest OS in their container file will result in the entire file being backed up.  This can increase the backup time a great deal.  The same effect will occur if you have any very large file that is always changing, such as a huge log file that has items appended to its tail end on a regular bases.
With respect to scheduling, there are utilities available to change the scheduling anyway you wish.  Search over at MacUpdate.com
Regarding the relative efficiency for Time Machine versus rsync, there is no comparison between the two.  Rsync is hands down more efficient in terms of CPU and network usage.
A well working Time Machine WILL be more efficient that rsync (and I am a heavy rsync user, as well as a Unix file system developer during the day).  Time Machine uses Spotlight to keep track of changed files, so that when it is time to do a backup Time Machine does not need to look for changed files, it has a list handed to it from Spotlight.
Rsync needs to scan the entire file system on BOTH the source AND destination system reading every file's metadata to get the modification date and compare that between the source and destination system.  That in and of itself is very demanding on the disk drives of BOTH source and destination systems.
I use rsync to backup my Mom's system across the internet, I use rsync to backup several systems at work, I rsync to transfer software trees to build servers, I use rsync to keep my personal scripts and utilities in sync on multiple systems.  Rsync is great, however, it is not as efficient, and most definitely not as easy to use as Time Machine.
So if you are having problems, there is something else going on, as most users do not experience what you are seeing.  Including me, as I also use Time Machine on several systems.
For example, as mentioned above, huge files that get modified on a regular bases.
Since you are going over a network, it is possible you have network interference that is reducing your effective trasnfer speeds.  Using 802.11g vs 802.11n w/5GHz frequences.  A network sniffer (iStumbler, KISMac, ...) would be able to tell you if you have neighbors using the same channels, or a channel that is within 5 of yours that might be causing interference.
As for shutting down vs sleeping your Mac, I do not know if that would or should affect your Time Machine backup performance.  I would be looking at other things.
However, I might speculate that maybe Mac OS X thinks your Time Machine container file stored on the Time Capsule is damaged, so its is running 'fsck' when Time Machine mounts the volume.  This would consume a great deal of time.  You could run Applications -> Utilities -> Activity Monitor and see if there is an fsck_hfs program running while your excessively long Time Machine backup is in progress.
Finally, if you prefer rsync, you can always just use the Time Capsule as a Network Attached Storage (NAS) and backup using rsync from your Mac to the Time Capsule.  You could even use Carbon Copy Cloner which is a very nice GUI wrapped around rsync, and as a bonus the CCC developer always ships the most recent Mac OS X compatible rsync as part of the CCC distribution.  If you want rsync AND you want the multiple generation incremental Time Machine backup features, you can either roll your own using the rsync --link-dest option, or find one of the Unix scripts, such as rsnapshot (or similar) that wrap a script around rsync --link-dest (almost as good as a Time Machine incremental backup).
Bottom line.  You have a problem.  It is specific to your situation.  I have listed several possible reasons for what you are seeing, there could be more.  If you could provide feedback on some of the things I've mentioned, maybe we could help figure out what is going on.