HP 9000 Virtual Library System - Manual (Page 226)

Deduplication Issues
Solution Possible causes Symptom
Consider using cartridges that are
smaller than the sum of your daily The VLS does not free up storage on
a cartridge until: The VLS is not deduplicating the
backup jobs.
backup jobs so the cartridges
deduplicate sooner.
• At least two full backups of the
same policy exist on different
cartridges
•
The delta-differencer has processed
all of the backup sets on the
cartridge
•
The cartridge is physically full
None The compression ratio depends on the
amount of data changed between the The deduplication compression ratio
is low.
backup sets. In addition, not all data
is deduplicated. For example, files less
than 32 KB in size and backup sets
less than 1 MB are ignored. If your
data sets do not change significantly
between backups, or if they contain
many small files, the compression ratio
may be low. This is expected behavior
and does not indicate a problem.
In time, the ratio will improve as more
backup sets are deduplicated. After 50 versions of a backup set have
been deduplicated, the VLS The deduplication compression ratio
was fine, but suddenly went down
significantly.
automatically restarts the deduplication
process as though starting from
scratch. As a result, the compression
ratio will drop.
After 50 versions of a backup set have
been deduplicated, the VLS The restore performance will continue
to degrade as you restore older and
older versions of a backup. The restore performance is degrading.
automatically restarts the deduplication
process as though from scratch. The
restore performance will then improve
because the restore versions are more
recent.
226 Troubleshooting