Problem with Compression Ratio

[Bearcules]

At my company we use LTO2 tapes with a 200/400 GB capacity to back up our data nightly.  Until recently we consistently got compression ratio's of close to 2:1 on these tapes using hardware compression.  Recently we got a new set of tapes which at best would get 1.6:1 compression.  At first I thought that this was a tape related issue because it seemed to only happen on these new tapes, however, since then the compression ratio on the new tapes has fallen to 1:1, and the compression ratio on the older tapes has fallen to 1.5:1. 

Is it possible that if the new tapes were faulty it could damage the drive and cause the compression ratio to drop?  Has anyone else had this type of issue?

[Kiran_Bandi]

No, compression rate depends upon the type of data you are backing up. If you are backing up data which already compressed, you may not be getting any compression.

Try the following to verify the compression: How to perform a test to verify compression http://www.symantec.com/docs/TECH78389.

Regards...

[Bearcules]

Thank you for the quick response!

Is there a reason it would vary from day to day?  We are backing up roughly the same data every day, and as far as I know it is not compressed on the servers.

[Colin_Weaver]

Just be aware data compression does not just depend on whether you have enabled it on the server drives/volumes - jpeg and mpeg files are already compressed - hence file types can make a huge difference. However you should not see day to day changes unless you have large amounts of data changing daily-

[Bearcules]

I tried doing the compression test with the older tapes and the new tapes as directed by Kiran Bandi: http://www.symantec.com/docs/TECH78389.

The results were the same with both, and the compression was 45.5:1.  So does this mean there is nothing wrong with the new tapes that is causing the compression problems?  Could it just be a coincidence that the issues have been happening on days when we back up with the new tapes?

The vast amount of data that is being backed up changes little from day to day.  Could users accessing the servers during back up using VPN influence the compression at all?

[Kiran_Bandi]

The results were the same with both, and the compression was 45.5:1.  So does this mean there is nothing wrong with the new tapes that is causing the compression problems? 

Nothing wrong with the tapes or tape drive.

The vast amount of data that is being backed up changes little from day to day.

Is your backups spanning to multiple tapes? If so compression ratio may differe from tape to tape depending the type of data written on those particular tapes. And also the amount of data written to the tapes.

Regards...

[pkh · Accepted solution]

As the others have said, your tapes do not play a part in the compression.  It is the data that determine what compresssion ratio you get.  You might want to expand your joblog and check which resource is not compressing well and see what you can do about it.

You might want to read my article on compression

https://www-secure.symantec.com/connect/articles/compression-short-explanation 

[Bearcules]

I think we narrowed the problem down to a set of files on one of our servers.  Thanks everyone, for all your help!