Backup exe not compressing the data

[Rayen]

Hi all,

Im using a dell Powervault LTO-3 tape library.

My data which i want to backup is 590 GB.

Im using a ultruim 3 tape which is 400GB/800 GB.

I also have to using Software encryption and hardware compression.

I have to use 2 tape drive to backup the data.

I have 2 questions:

1.Why the data isn't being compressed so that it can fit on one tape sinds the tape is 800 GB compressed.?

2.Is the combination which im using Software ebcryption and hardware compression a good combination?

Regards,
Rayen

[CraigV]

Hi there,

It should be Software compression, otherwise Hardware compression if you're doing this within BE. If you're compressing the data with a 3rd party compression tool BEFORE it gets backed up, you'er running the risk of the data decompressing during the backup, which explains why you're not getting that data onto the tape.

There are times when already-compressed data "rehydrates", meaning you're backing up more than normal. What you need to check is that the tape drive has compression enabled, and select Hardware, otherwise Software instead of the other way around. This way you're using the drive to compress...not system resources.

Thanks!

[Colin_Weaver]

Encrypted data does not compress well as encrypted data is randomised and does not contain many matching bytes that will match a compression algorithm

EDIT:see suggestions in

http://www.symantec.com/docs/TECH83239

[sksujeet]

Also it is always not possible to get 1:2 compression depending upon the data that you are backing up. So if tape is writing around 500 to 600 gb that is fairly good.

[pkh]

1.Why the data isn't being compressed so that it can fit on one tape sinds the tape is 800 GB compressed.?

This is a marketing ploy.  In real-life, a 2:1 compression ratio is very rarely achieved.  Normally, you should get a compression ratio of about 1.2 - 1.3  which means that your data would probably need 2 tapes.

See my article on compression

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

2.Is the combination which im using Software ebcryption and hardware compression a good combination?

This is a bad combination.  Again see my article above for the explanation.  If you want encryption and compression, either use hardware or software for both, but not your combination.