HP 12000 HP StorageWorks 12000 Gateway Virtual Library System User Guide (AH81 - Page 227

Deduplication Issues Symptom The VLS is not deduplicating the backup jobs. Possible causes Solution 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 processed all of the backup sets on the cartridge • The cartridge is physically full Consider using cartridges that are smaller than the sum of your daily backup jobs so the cartridges deduplicate sooner. The deduplication compression ratio is low. The compression ratio depends on the amount of data changed between the 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. None The deduplication compression ratio was fine, but suddenly went down significantly. After 50 versions of a backup set have been deduplicated, the VLS automatically restarts the deduplication process as though starting from scratch. As a result, the compression ratio will drop. In time, the ratio will improve as more backup sets are deduplicated. The restore performance is degrading. The restore performance will continue to degrade as you restore older and older versions of a backup. After 50 versions of a backup set have been deduplicated, the VLS automatically restarts the deduplication process as though from scratch. The restore performance will then improve because the restore versions are more recent. HP StorageWorks 12000 Gateway Virtual Library System User Guide 227