BE 12 Compression

[Gary_Hurst]

Hi folks 

A full backup for me is about 600gb so I purchased Ultrium LT0 3 tapes 400gb/800gb to run in my hp MSL6000 series tape library. I have enabled compression via the devices tab but a second volume is requested after writing less than 600gb. Why would it do that ?? Surely it should write up to 800gb with compression enabled ??

The media statistics don't seem to make sense;

Used capacity: 373.2gb of 390.9gb

Total capacity: 390.9gb

Compression ratio: 1.5:1

Bytes written: 563gb

Why would it record a total tape capacity of 390.9gb but then say that 563gb has been written ?? How is that possible ??

Anyone else having these isuues or know the answer ?? Thanks.

Gary

[Steve_W_]

With Compression 800GB is not guaranteed.  Compression is based off of the data that you are backing up.  A SQL database is not going to compress as much as a standard text file.  If you are backing up 600GB of data and it can only fit 563GB of data on the tape then it will ask for a new tape.  1.5 to 1 compression is about average for most environments because most environments have Exchange and SQL and other files that are already compressed as far as they can go.  Compression is not controlled by the software, but by the hardware in this case.  Also, verify that the backups are set to overwrite media instead of "append and then overwrite if no appendable media is available."  This could also be a reason why it is grabbing a second tape because it is appending to the end of one tape and then grabbing a second tape to continue the rest of the job. 

Message Edited by sw-symc on 10-09-2008 05:26 AM

[Hywel_Mallett · Accepted solution]

What sw-sync said!

Also see http://www.backupexecfaq.com/articles/problems/media-capacity-problems.html

[Gary_Hurst]

OK, I will be very popular (not!) when I ask for money to buy another set of tapes to complete the backup cycle.

Thanks for your responses.

Gary