Time Machine does not work well with NAS devices, even those that indicate Time Machine compatibility. An NAS may appear to work, only to find that your backups are corrupted when needed. Such complaints are very common on this site. It is best to use a Time Machine configuration suppored by Apple, since there is no guarantee a future OS X update or upgrade will result in corrupting your NAS backups.
You may find that TM is performing excessively large backups without justification. To fix that read the following:
Turn off Time Machine in Time Machine's Preferences. Eject and disconnect the backup disk, if it is locally connected (not a Time Capsule).
Select the following line (triple-click to select the entire line), then control-click, and from the contextual menu that appears, select Services > Reveal in Finder:
/Library/Preferences/com.apple.TimeMachine.plist
Drag the selected file directly to the Trash. You will need to authenticate.
This procedure will not delete your existing backups any differently than Time Machine would normally perform that task.
Reconnect your backup device, then from Time Machine's Preferences, turn on Time Machine, select your backup device, then select Back Up Now from the Time Machine icon. TM will remain in "Preparing Backup..." for a long time. When it eventually begins backing up, you may notice that the "backing up xxx of yyy" numbers will appear to change unpredictably. That's normal, and TM activity will return to normal after the initial backup of the Mavericks installation.
