Mac OS X 10.5: Time Machine preferences may display "Preparing" for a longer time
Symptoms
Time Machine keeps track of files and folders that have changed since your last backup so that it only backs up those files and folders. If Time Machine loses track of files and folders that have changed since the last backup, it will compare an "inventory" of your current data to an inventory of your backup. When this happens, Time Machine preferences displays a "Preparing..." status message for a longer period of time.
Products Affected
Time Machine, Mac OS X 10.5
Resolution
After the comparison is complete, Time Machine backs up new and changed files. Try not to interrupt Time Machine when it is "Preparing" or when it is backing up files because that could cause the next backup to take longer.
Additional Information
Depending on how large your data is and how large your backup is, and how fast the connection is to your backup disk, this "Preparing" process may take significantly more time.
How can Time Machine "lose track" of changed files and folders?
Time Machine may lose track of files and folders that have changed if your Mac is not shut down properly, or if a mounted disk is not removed properly by ejecting it first. This may also happen if you use your computer for several days without performing a Time Machine backup (by not having the disk connected, for example).