Time Machine same backup size every time

Question

Anyone have any idea why Time Machine would backup the same amount every time? Every hour mine backs up 1.8 GB, unless I've added more than that to my hd.
I only back up the internal drive on my macbook to a 500 GB Time Capsule via wifi (802.11n only, 5GHz). Not that I figured it would make a difference, but it still does it if backed up via ethernet.
I've also noticed that as soon as it completes the backup, it will backup all over again - and not because an hour has passed. I'm not sure if it does this every time (but I think i does), or if it does it more than twice when it happens.
Thanks in advance!

Answer 1

See if the following might give you some ideas as to why...
*_Incremental Backups Seem Too Large!_*
Open the Time Machine Prefs on the Mac in question. How much space does it report you have "Available"? When a backup is initiated how much space does it report you need?
Now, consider the following, it might give you some ideas:
Time Machine performs backups at the file level. If a single bit in a large file is changed, the WHOLE file is backed up again. This is a problem for programs that save data to monolithic virtual disk files that are modified frequently. These include Parallels, VMware Fusion, Aperture vaults, or the databases that Entourage and Thunderbird create. These should be excluded from backup using the Time Machine Preference Exclusion list. You will, however, need to backup these files manually to another external disk.
If you do a lot of movie editing, unless these files are excluded, expect Time Machine to treat revised versions of a single movie as entirely new files.
If you frequently download software or video files that you only expect to keep for a short time, consider excluding the folder these are stored in from Time Machine backups.
If you have recently created a new disk image or burned a DVD, Time Machine will target these files for backup unless they are deleted or excluded from backup.
*Events-Based Backups*
Time Machine does not compare file-for-file to see if changes have been made. If it had to rescan every file on your drive before each backup, it would not be able to perform backups as often as it does. Rather, it relies on a process called FSEvents. This is a system log that records changes that occur with all the directories on your Mac. Moving / copying / deleting / & saving files and folders creates events that are recorded in this log. At the beginning of each backup, Time Machine simply looks at this log to determine what has changed since the last backup. [http://arstechnica.com/reviews/os/mac-os-x-10-5.ars/14]
Installing new software, upgrading existing software, or updating Mac OS X system software can create major changes in the structure of your directories. Every one of these changes is recorded by the OS as an event. Time Machine will backup every file that has an event associated with it since the installation.
Files or folders that are simply moved or renamed are counted as NEW files or folders. If you rename any file or folder, Time Machine will back up the ENTIRE file or folder again no matter how big or small it is.
George Schreyer describes this behavior: “If you should want to do some massive rearrangement of your disk, Time Machine will interpret the rearranged files as new files and back them up again in their new locations. Just renaming a folder will cause this to happen. This is OK if you've got lots of room on your backup disk. Eventually, Time Machine will thin those backups and the space consumed will be recovered. However, if you really want recover the space in the backup volume immediately, you can. To do this, bring a Finder window to the front and then click the Time Machine icon on the dock. This will activate the Time Machine user interface. Navigate back in time to where the old stuff exists and select it. Then pull down the "action" menu (the gear thing) and select "delete all backups" and the older stuff vanishes.” (http://www.girr.org/mac_stuff/backups.html)
*TechTool Pro Directory Protection*
This disk utility feature creates backup copies of your system directories. Obviously these directories are changing all the time. So, depending on how it is configured, these backup files will be changing as well which is interpreted by Time Machine as new data to backup. Excluding the folder these backups are stored in will eliminate this effect.
*Backups WAY Too Large*
If an initial full backup or a subsequent incremental backup is tens or hundreds of Gigs larger than expected, check to see that all unwanted external hard disks are still excluded from Time Machine backups. Time Machine will attempt to backup any hard disk attached to your Mac, including secondary internal drives, that have not been added to Time Machines Exclusion list.
This includes the Time Machine backup drive ITSELF. Normally, Time Machine is set to exclude its’ own backup disk by default. But on rare occasions it can forget. When your backup begins, Time Machine mounts the backup on your desktop. (For Time Capsule/AirDisk users it appears as a white drive icon labeled something like “Backup of (your computer)”.) If, while it is mounted, it does not show up in the Time Machine Preferences “Do not back up” list, then Time Machine will attempt to back ITSELF up. If it is not listed while the drive is mounted, then you need to add it to the list.
*Recovering Backup Space*
If you have discovered that large unwanted files have been backed up, you can use the Time Machine “time travel” interface to recovered some of that space.
Launch Time Machine from the Dock icon.
Initially, you are presented with a window that represents “Today (Now)”. DO NOT make changes to file while you see “Today (Now)” at the bottom of the screen.
Click on the window just behind “Today (Now)”. This represents the last successful backup and should display the date and time of this backup at the bottom of the screen.
Now, navigate to where the unwanted file resides.
Highlight the file and click the Actions menu (Gear icon) from the toolbar.
Select “Delete all backups of <this file>”.
*FileVault / Boot Camp / iDisk Syncing*
Note: Leopard has changed the way it deals with FileVault disk images, so it is not necessary to exclude your Home folder if you have FileVault activated. Additionally, Time Machine ignores Boot Camp partitions as the manner in which they are formatted is incompatible. Finally, if you have your iDisk Synced to your desktop, it is not necessary to exclude the disk image file it creates as that has been changed to a sparsebundle as well in Leopard.
Let us know if this resolved your issue.
Cheers!