Time Machine Endless/Very Slow Backup

Question

Hi All,
I've recently encountered a situation in which Time Machine never seems to think it's finished backing up. In the screenshot below you'll see that it's backing up the exact same amount of data from my HD and an external drive called "Movies" (first time 234.6mb & then started again and updated 41.5mb). The thing is, absolutely nothing was changed in the "Movies" drive, it hasn't been touched or synced with anything since the last backup. I'm thinking that's some kind of clue, but not sure what kind of clue it is. I have done many of the things listed here (including "full reset of time machine" and :
https://discussions.apple.com/thread/2057525?threadID=2057525
As well as run Clean My Mac, Repaired Permissions, verified & repaired "Movies" (it was OK), and run Yasu.
Last backup ran for :31min and nothing much had changed. This just started happening recently as outside of major activity TM used to back up in just a few minutes. The good news is the backup was completed successfully, but would love to know what anybody thinks might be the culprit. Oh also backing up to external HD with 1.3TB avail (MB Pro with 750gb HD).

Answer 1

Following the advice of the great Pondini and others, I found a series of steps that worked to correct this situation on ALL my machines!
Here is a link to Pondini's excellent troubleshooting site, which is where I found most of these steps. You might consider just going there and ignoring my steps below, because he is definitely the expert in this field.
http://Pondini.org/TM/Troubleshooting.html
The below is kind of a "nuclear option." Not sure which step does what, but know that after doing all of them my incremental backups are now running at :10 - :20 SECONDS where they were taking 40 minutes to an hour before (be forewarned, it takes a while to do all this).
Turn TM off!
Use Disk Utility "repair disk" function on ALL disks (TM, Mac HD, any others that get backed up). Open Disk Utility, select disk, then select "repair disk."
Instead of #2, you might consider using Disk Warrior to rebuild your directories. It costs about $100, but it's an extremely valuable tool and can save your sauce in many ways. Honestly I would advise buying DW and doing that instead of the Disk Utility option, which, while free, does not seem to be as robust a solution.
An alternative to repairing the TM drive is to just start over with a clean, correctly formatted drive (see below). You should still repair/rebuild your MacHD and any other drives that get backed up, though.
Trash this file: com.apple.TimeMachine.plist (found in MacHD > Library > Preferences).
Repair Permissions on MacHD
In System Preferences > Spotlight > Privacy add MacHD (your main/boot drive) to Privacy pane, close system preferences, then reopen and remove it (add and remove using -/+ at the bottom of the window). This will force Spotlight to re-index MacHD (wait until it's finished to do anything else).
Make sure your TM HD is formatted properly: should be using the GUID partition table (even if it's not partitioned) and be formatted Mac OS Extended (Journaled). These settings will appear at the bottom of the Disk Utility window when you select the HD itself (not by its volume name). If you are not formatted this way, it's recommended that you reformat. Unfortunately, this means your existing backups will be no more (unless you have another drive you can use and preserve the old one until you're safely backed up again).
Reset PRAM. Restart your mac and hold down these keys simultaneously: option command p r. Hold them down until you hear the second "restart" chime.
Enter TM preferences and re-select TM disk (when you trash plist TM will "forget" the drive, but all the info is still on the drive) but don't let TM run yet.
In TM options make sure any disks you prefer to exclude/include are either entered or not (TM HD should always & automatically be excluded)
In System Preferences > Spotlight > Privacy make sure TM disk is excluded from Spotlight (using +/- as above).
Finally, enter Time Machine and go through your backups to see if there are any backups that shouldn't be there: should be one backup every hour for the past day, one backup every day for the past month and weekly backups before that. If you find more than one backup on a day 3 weeks ago, for example, delete all but the most recent one for that date (on the window of the backup you want to delete you should see the "gear" icon with a dropdown arrow - click on it and select "delete backup."). You have to delete them one at a time so depending on how many you find & how big your backups are this step can take a very long time but it's critical to making sure TM doesn't get hung up on the "finishing" phase. If TM looks back in time and finds more backups than it wants it's supposed to just delete them but it doesn't always work that way and that's one of the issues that can make the finishing stage of the backup take forever.
Restart your Mac.
Restart TM & hope for the best.