I think if you turn on software compression this only applies to the data 
"in-flight", i.e. it is compressed by the client but decompressed by the 
server, regardless of the type of storage unit.  It is designed to be used 
for slow links, where the CPU overhead at each end is more than 
compensated by the reduced transmission time.

One a LAN it would be pointless unless you had a fast client on a 10Mb 
link.  Even on a WAN many WAN routers use compression to improve 
throughput.

There are now VTLs that compress the data going to disk; they always have 
a bit of a gamble as to how well they can mimic the way the real tape 
compresses data; I'm told they just use very conservative estimates, to 
make sure the disk image will fit on the tape.

William D L Brown




"Bob Stump" <stumpb AT michigan DOT gov> 
Sent by: veritas-bu-admin AT mailman.eng.auburn DOT edu
19-May-2006 15:41
 
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Subject
[Veritas-bu] compression to disk staging unit






Is it wrong to use software compression in a policy that uses a disk 
staging unit for the storage unit? 
Will this result in slower migration or negative compression during the 
migration phase to a tape drive that uses hardware compression?