Deduplication Issues - HP StorageWorks 12000 - Virtual Library System EVA Gateway User Manual

Deduplication Issues

Symptom
The VLS is not deduplicating the
backup jobs.
The deduplication compression ra-
tio is low.
The deduplication compression ra-
tio was fine, but suddenly went
down significantly.
The restore performance is degrad-
ing.
Possible causes
The VLS does not free up storage
on a cartridge until:
• At least two full backups of the
same policy exist on different
cartridges
• The delta-differencer has pro-
cessed all of the backup sets on
the cartridge
• The cartridge is physically full
The compression ratio depends on
the amount of data changed
between the backup sets. In addi-
tion, 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.
After 50 versions of a backup set
have been deduplicated, the VLS
automatically restarts the deduplic-
ation process as though starting
from scratch. As a result, the com-
pression ratio will drop.
The restore performance will contin-
ue to degrade as you restore older
and older versions of a backup.
Solution
Consider using cartridges that are
smaller than the sum of your daily
backup jobs so the cartridges dedu-
plicate sooner.
None
In time, the ratio will improve as
more backup sets are deduplicated.
After 50 versions of a backup set
have been deduplicated, the VLS
automatically restarts the deduplic-
ation process as though from
scratch. The restore performance
will then improve because the re-
store versions are more recent.
HP StorageWorks 231