On Mon, 3 Nov 2003 at 3:06pm, Jason Lavigne wrote

> I have a Adic VLS DLT7000, this is a 7 tape library with a DLT7000 drive
> and I would like to be able to use the full 70GB available in each tape,
> however according to the following I feel this is not happening:

Manufacturers lie, to their advantage.  How much compression the hardware 
gets is dependent on your data.  If it's all binary image data, e.g., it 
will *expand* when run through hardware compression.  If it's all text 
files, it'll compress to about 10% of original size.  In general, for a 
mix of data, I've found that 2X is rather generous.

> Does anyone have a tapetype configuration that uses hardware compression
> and the full 70GB?

Amanda uses the tapetype only to see how much tape it can use in a night.  
If you're using hardware compression, you must estimate how much your data 
will compress and increase the tapelength appropriately.  If you keep 
hitting EOT, you assumed too much compression.

If you use software compression, amanda keeps track of how much each DLE 
compresses, and uses this info to more efficiently plan.

-- 
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University