Jeffrey,
Consider these factors regarding an extended period of "Preparing...":
*Recent Crash or Other Major System Event* (Deep Traversal)
The reasons for this process are described in an article by George Schreyer. “During the preparation step it checks the FSEvents log for consistency. If it determines that something isn't quite right it has to rescan the whole disk. This can take quite awhile. A full rescan is always triggered by a crash, an unplanned shut down event or by booting from some other bootable disk between backups…. After a crash, Time Machine must scan the whole disk to determine what it has to do because it cannot trust the information that it left behind. Connected via an Ethernet connection, this phase would typically take 20 minutes on an older PowerBook. Being connected wirelessly stretches this phase out to over 3 hours.” [http://www.girr.org/mac_stuff/backups.html]
According to the following KB article it can sometimes take a very long time if Time Machine begins this “deep traversal” and has to compare data inventories. This may apply to your situation, particularly if many Gigs of data are involved. (
http://support.apple.com/kb/TS1516)
*Software Updates*
Installing new software, upgrading existing software, or updating Mac OS X system software can created major changes in the structure of your directories. Time Machine will backup every file that has changed since the installation.
*Anti-Virus Software*
Running anti-virus software can interfere with the backup process. Either disable it altogether, or try the suggestion outlined here, “If you use third-party anti-virus scanning software and have issues, make sure your Time Machine back up folder (Backups.backupdb on the Time Machine disk) is excluded from virus scanning.” (
http://support.apple.com/kb/TS1516)
*Stalled .inProgress Files:*
It may be that the previous backup attempt was ungracefully interrupted leaving remains that Time Machine can’t deal with.
Open your Time Machine drive.
Open the folder labeled “Backups,backupdb”.
Now open the folder containing backups of the computer in question.
Are there any “.inProgress” files there. Delete them.
(For Time Capsule Users)
Select the TC in the SideBar of the Finder window.
Click "Connect as...". Enter your TCs password.
Double click the blue folder that appears in the finder window. The sparsebundle should now be visible.
Double click the sparsebundle and then click “Skip” in the checksum message.
Once “Backup of (Users Computer)” mounts in the Sidebar, click on it and open the “.backupdb” folder. Now open the folder containing backups of the computer in question.
Are there any “.inProgress” files there. Delete them.
Unmount the sparsebundle, then unmount the TC, and try backing up again.
Let us know if any of the suggestions above helped.