Compression Question

[Ryan_Donnelly]

I'm running Backup Exec 10.0 with a Dell PV132T and LTO2 200/400 tapes. I have tapes that show over 3:1 compression and up to 638 GB written. Could these stats be correct? Specs for the tapes and drive show a maximum of 2:1 and 400 GB per tape.

[Keith_Langmead]

Well while it's certainly unusual, depending on the type of data you're backing up it is quite possible to have a ratio that high.

There is no upper or lower limit on the amount of compression, it purely depends on the type of data you're backing up. For instance files which are already compressed like executables, jpeg images, zip files etc will get little or no compression, while text files, bmp images etc will get a very high ratio.

The 2:1 ratio normally stated on most tapes is basically a number someone in the tape industry plucked from the air, and has little or no relevance to reality.

[Ken_Putnam]

2:1 compression is pure marketing BS, not engineering promise. Most people will see in the 1.3-1.4 range, but depending on data type it can go considerably higher. I once had a sparsely populated SQL database that would compress at about 8:1, but the average for all SQL servers was closer to 1.9:1

Doesn't directly address your problem, but see http://support.veritas.com/docs/199542

Message was edited by:
Ken Putnam


Sorry for repeating what you said Keith - got distracted while the response form was open

[Ryan_Donnelly]

The tapes in question were backups of MS SQL. Thanks for the replies.