Tape not compressing data as expected...

[simple99]

Hi,
We have LTO3 400GB/800GB tapes but I notice that the tapes get full when reaching around 300-400GB.

I have checked the Hardware compression setting is enabled in Storage Policies copy properties.
The subclient is set to compression on the 'Client' side
The Tape library properies has 'Ultrium 3' set as default media.

Am I missing something else...

Thanks

 

[birky]

turn off client software compression and only have hardware compression enabled

 

[simple99]

thanks birky,
should I use 'MediaAgent' compression atleast or does that not matter.

Or is the idea that I turn off all compression on the 'Client' and 'Media Agen' side and send uncompressed data to the Tape Library, so that the Hardware takes care of compression at that stage ?

 

[simple99]

Just adding to my previous comment, the setup of our system is:

Subclient is on a physically different server
MediaAgent is on the CV server which has a SCSI connection to Tape Library.

 

[birky]

If going directly to tape then you shouldn't have any software compression switched on....select Hardware compression instead.

Software compression is mainly intended for;-

Client side compression - for sending data across WAN links
Media Agent compression - for writing to disk if you want to save space.

 

[simple99]

Thanks for the info birky.

excellent advice.

I'll give that a go.

cheers

 

[simple99]

birky
After re-reading your advice.

The data from the subclient is not going directly to Tape.

It goes from Subclient to disk then aux copy to Tape.

In this case should I have Media Agent Compression ?
Along with Hardware Compression on Tape media ?

thanks.

 

[birky]

You could do but, as the data is already compressed you aren't going to see any difference with the Hardware compression as software compressed data isn't uncompressed before it's written to tape.

If the data has already been compressed, the compression figure may actually be negative. Some data, including graphics files or archived disk partitions, is compressed as it is written. Not only can't tape systems further compress already compressed data, but the attempt can result in files that are larger than the originals. Likewise, although both backup software and tape drives can compress data, the rule is that you only use one compression method at a time. In general, you can expect the tape hardware to do a slightly better job of compression than the software compression.

You need to make a decision as to which is more important, saving space on the maglib or reducing tapes.

 

[simple99]

birky
Thanks again for the detailed advice.

 

[dutchtreat]

I think 500GB is valid using hardware compression with LTO3.

 

[Frbutler]

I have sqeezed 600gb onto a LTO2 before.
I would hope to get better compression on LTO3