Housekeeping; Restoring From A Recipe File - HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual

Figure 28 Restoring from a Recipe File
.
1. The first hash in the recipe file is located in the index, which provides the location on disk of the
original chunk of data.
2. The original chunk is found and returned to the restore stream.
3. The D2D moves on to the second hash, and repeats this process for all subsequent hash values
in the recipe file until the entire file is returned to the restore stream.

Housekeeping

If data is deleted from the D2D system (e.g., a virtual cartridge is overwritten or erased), any unique
chunks only applicable to the deleted data will be marked for removal and non-unique chunks will
be de-referenced. The process of removing chunks of data is not an inline operation because this
would significantly impact performance. Instead, the process of "housekeeping" runs as a background
operation on a per cartridge basis and runs as soon as the cartridge is unloaded and returned to its
storage slot.
While the housekeeping process can run as soon as a virtual cartridge returns to its slot, this could
cause a high level of disk access and processing overhead affecting other operations such as further
backups, restores, tape offload jobs, or replication. In order to avoid this, the housekeeping process
checks for available resources before running; if other operations are in progress the housekeeping
will delay to prevent impacting performance of other operations. The delay is not binary (i.e., on or
off), so even if backup jobs are in process some low level of housekeeping will still occur which may
have a slight impact on backup performance.
Housekeeping is important in maximizing the deduplication efficiency of the appliance. Therefore,
you must ensure that it has enough time to complete. Running backup, restore, tape offload, and
replication operations with no break will result in housekeeping never completing. As a general rule,
housekeeping needs 30 minutes per day for every 100 GB of data overwritten on a virtual cartridge.
For example, if on a daily basis the backup application overwrites two cartridges in different virtual
libraries with 400 GB of data on each cartridge, the system will need two hours of inactivity over the
course of the next 24 hours to run housekeeping in order to de-reference data and reclaim any free
space.
72 D2D Systems