At 10:22 AM 9/29/99 -0600, Alan Cheski wrote:
>Howdy, we have Novell and Unix ADSM clients. The unix clients backup data to
>ADSM using compression. The Novell clients do not use compression but I think
>Netware uses a compressed file system format anyway. On our ADSM server,
someone
>setup the DLT deviceclass with a format of DLT35C, meaning to do hardware
>compression. I am thinking that we should not be doing hardware compression
>since we already backup compressed files. I believe it is possible to
increase
>file sizes in some cases by doing double compression. Should we turn off
>hardware compression?
>
>Alan Cheski
>Gulf Canada Resources

If you are using ADSM client compression (not Netware, but ADSM), then you
should disable DLT compression.  Compressing twice results in lower
utilization of the tapes (expansion).  I ran an analysis on this with an
early version of ADSM v3 and DLT 7000 drives and found that double
compression results in data expansion (overall).  It is my view that
compressing at the client should be done where feasible, since it lessens
resource usage of your network, and of moving data around on the ADSM
server (reclaims, migration, etc).

..Paul