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NOTE:
Deduplication takes place after the data has been processed to the backup tapes. Therefore, any data
backed up to compression-enabled virtual tape drives (both software and hardware compression) is
compressed before it is deduplicated.
How it Works
The following is an overview of the deduplication process. See the HP StorageWorks VLS and D2D
solutions guide for more detailed information.
1.
When a backup runs, a data grooming exercise is performed on the fly. Using meta-data attached
by the backup application, data grooming maps the content or "objects" of the backup, and
assembles a content database. This process has minimal performance impact.
2.
After the scheduled backups have completed, the content database is used to "delta-difference"
(compare) objects in current and previous backups from the same hosts. There are different levels
of comparison. For example, files may be compared using a strong hashing function, while other
objects may be compared at a byte level.
3.
When duplicate data is found in an older backup, it is replaced by a pointer to the most recent
copy of the same data. Because the most recent backup is a full version, you achieve the fastest
possible restores.
4.
Users can enable an optional, secondary integrity check of data
between the deduplicated version with pointers and its original version. With this option, the
original backup is only replaced upon successful completion of the comparison.
5.
Space reclamation occurs when duplicate data from previous backups is removed from the disk.
This can take some time, but results in previously consumed capacity being returned to a free
pool on the device.
Getting Deduplication Running on the VLS
Considerations
To make the most of the deduplication benefits, review these considerations before setting it up on
your VLS system:
•
Virtual cartridge sizing — The system cannot deduplicate versions of a backup that are on the
same cartridge; the versions are not deduplicated until a new version is written to a different virtual
cartridge. Therefore, you want the cartridges to be sized big enough to contain an entire backup
job and to prevent too many backup jobs from piling up on the same cartridge, but small enough
that you are not wasting overall cartridge space.
•
Additional nodes — For systems with long backup windows, you may want to include additional
nodes to speed up the post-processing deduplication.
•
Additional capacity — Because you must store two full backups before the delta-differencing begins,
you may want to include additional disk capacity at least the size of the sum of the backups.
Installing the Firmware
The deduplication feature requires an upgrade to the VLS firmware version 3.0 or higher. Download
the VLS Firmware and Quick Restore CD Image appropriate for your VLS system from the HP website,
and burn it to a CD. Then follow the instructions for using the quick restore CD.
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Deduplication
a byte-for-byte comparison
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