Sun Microsystems Virtual Tape Library User Manual page 54

Managing virtual libraries
both the needed long‐term storage capacity and the fastest possible transfer to tape
media. Compression hardware cannot further compress data that has been
compressed by software, so the end‐to‐end backup process is significantly slower.
On the other hand, the VTL software compression feature is valuable when it is truly
needed:
when data is stored on the appliance long‐term, rather than cached pending
migration to long‐term storage on physical tape
when data has to be replicated across a slow WAN link.
3. If you plan to use tape caching, use the spinner control to adjust the Tape
Caching Policy Disk Capacity Threshold to 85% (
When using automatic tape caching, you have to make sure that the disk never fills
up, preventing you from creating new virtual volumes. The 75% threshold has been
found to offer a good margin of safety.
4. Press OK (
Stop here.
40 VTL User Guide • May 2008
C
above).
E
E
D
85
above).
D
G • 96267