Time Machine – Fix ‘Waiting to Backup’ After ML Upgrade

The answer to your question is that the difference between these two codes (100 and 101) is not publicly documented by apple.

https://discussions.apple.com/message/23429422?ac_cid=op123456#23429422

However pondini.org/TM/D2.html gives reasons why and how to fix those errors, and the issues you are experiencing.

This isn't normal, but you have two options:

1. Just wait for all the processing to finish or error out.
2. Help the process along.

In this case, an initial backup can take a long time, but the way to help the process along is to delete the .../whatever.inProgress file. You could also try backing up to a new drive to make sure it's not a problem with the Mac as opposed to a problem with the backup drive or just a lot of changes to reconcile.

See this other answer for details.

https://apple.stackexchange.com/a/65801/5472

In cases where you run into this repeatedly, you can either try to isolate what folder takes so long to back up. On a first backup, I've tried to exclude the Users folder (or several folders at the base of the boot volume if they have more than 10 GB of data) to make sure that the filseystem is OK and the backup drive is OK. At that point, you will see backups taking a minute or so for each incremental backup. You can then relax the exclusion list and know if it freezes, then you have a problem in a specific folder.

The other way to attack this is run disk utility (or another tool) to repair the directory structure or make a back up using another tool and wipe the drives / restore them from backup.