Can't get Time Machine to back up server or attached drives

Question

Tried to use the search on these new discussion forums and was told I'm not authorized to search the server forums so sorry if this has already been asked and answered.
I'm having a serious issue trying to back up my Mac Mini Server running 10.6.7.  The setup is I've got the main server hard drive running the OS and storing user folders, the second drive is storing all server data (mail, ical, etc).  I have an attached Drobo that is where all our company's job files are stored.  I want to back up mainly the job files to an external USB drive via time machine.  I wouldn't mind having the server and data backed up as well but it's not as essential as the customer files.  I have not been able to get a successful Time Machine Backup of anything.  Time Machine will start backing up and hang after what seems like a random amount of data has been backed up.  This can range anywhere from a few hundred Gigabytes or a few Megabytes.  The last attempt has stalled out at 17MB of 518GB.
The troubleshooting I've done so far is to try to back up only certain things, so:
Format the USB Drive then try to back up only the main server hard drive, excluding all else.
Format the USB Drive then try to back up only the server data hard drive, excluding all else.
Format the USB Drive then try to back up only our jobs folder on the Drobo, excluding all else.
The result has been the same every time.  Seemingly random amount of data get's copied and then the backup hangs.  I do not get an error message the Time Machine backup icon on the menu bar just keeps spinning and I have the Time Machine window up that says:
Time Machine Backup
Backing up 269,376 Items
17.3 MB of 518.7 GB
This current attempt was to backup just our jobs folder and was started yesterday morning so it has been over 24 hours.  Disk Checks on the external USB drive come up with no errors every time I've scanned it.
Hoping someone has a solution.  One of the main reason's the company owner decided to get a mac server was how well time machine worked on his mac at home and the idea of being able to go back to pervious versions of customer jobs if necessary.

Answer 1

I agree with Sven.  I use TM to backup my server and have had EXCELLENT success.  I work in a school with many teachers that love to delete files and empty the trash on their user accounts.
>>facepalm<<
They promptly come-a-runnin' crying about how they've lost that ever important document.  Time machine to the rescue!
About the hanging problem...  I've see it as well.  I fixed it by finding the document that it was trying to back up.  I copied it to a USB stick and deleted said file from the server.
I ran the time machine backup again, and it worked!  I kindly asked the teacher to just remake the file in question.  Luckily it wasn't anything important.  I just chalked that one up to a corrupt or unreadable file.
Another thing to beware of.  DO NOT expect time machine to be able to do a complete system restore on OS X server.  It's great for getting those lost files while the system is up and running, but it will not work when trying to replace your Open Directory.  It might get stuck on MySQL, and Mail as well.  These databases are VERY finicky.  If you need to back up your OD database, open up server admin and select "Open Directory."
Click the "Archive" button at the top.
To the far right hand side of the "Archive in" field, click choose. 
Select the location that you want to save your archive to (the time machine drive will work) and click choose.
Click "Archive..."  Type the name for your OD backup and type a password if desired.  You don't need to have one. 
Lastly... Smile on the inside knowing that your OD is nicely backed up and safe!