Netmail Archive 6.x
Netmail optimizes space consumption for the email archives by collapsing multiple copies of attachments into a single instance. Therefore messages are now linked back to the same/single instance instead of each storing their own copy. This provides significant storage savings, as multiple studies have shown that attachments form the bulk of the email content and files are often sent to multiple recipients within an organization. However, working in this fashion has some consequences and it's important to keep these in mind when managing your archives.
Sharing attachment stores
In the Netmail administration console, at Archiving -> Storage tab, the administrator can define the Storage Locations. Within each, the administrator must specify where the attachments for this location must be stored. The device/path chosen need not be unique, and in fact, sharing a common device/path among locations is recommended to maximize de-duplication benefits.
ILM delete & expire jobs
ILM jobs can be used to prune data whose lifetime has exceeded the company's retention policy. These jobs will delete messages only; attachments are not touched since they may be shared with other messages that remain. Therefore it is common even after a substantial deletion job that only a fractional amount of space is recovered. The difference lays in the untouched attachments.
After an ILM job runs and deletes messages, some attachments may no longer be referenced by any remaining email. These attachments are referred to as being orphaned. Another job must be run in order to purge them and recoup the space they consume. On a Storage Management job find the option for "Orphaned Attachment Purge for SIS" on the Criteria tab. The orphaned attachment purge can be run periodically (eg. monthly) to clean up after the weekly ILM jobs.
During the scan for orphaned attachments, the files are cross-checked for references against ALL locations in the system, just in case the attachment store has been shared across more than one location.
Indexing is Critical
Orphaned attachment purge job relies heavily on the integrity & completeness of the indexes in order to determine if a file is eligible for deletion. Please make sure all locations are properly indexed before running this job or you risk substantial data loss!