Tape Library Emulation; Optimizing Rotation Scheme To Reduce Housekeeping - HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual

In addition, consider other operations running on the D2D. For example, if multiple backups finish at
different times, each may result in some housekeeping work. Add all of the data backup amounts
together to get an idea of the time that housekeeping will take.

Tape Library Emulation

Emulation Types
The HP D2D Backup Systems can emulate several types of HP tape library devices, and the maximum
number of drives and cartridge slots is defined by the type of library configured. However, performance
is not related to library emulation except in the ability to configure multiple drives per library and thus
enable multiple simultaneous backup streams.
Cartridge Sizing
The size of a virtual cartridge has no impact on its performance. HP recommends that cartridges are
created to match the amount of data being backed up. For example, if a full backup is 500 GB, you
should select 800 GB, the next larger configurable cartridge. If backups span multiple cartridges,
you risk a performance impact because housekeeping operations will start on the first backup cartridge
as soon as the backup application spans to the next cartridge.
Number of Libraries per Appliance
The D2D appliance supports creating multiple virtual library devices. If large amounts of data are
backing up from multiple hosts or for multiple disk LUNs on a single host, you should separate these
across several libraries (and consequently into multiple backup jobs). Each library has a separate
deduplication "store" associated with it, and reducing the amount of data and complexity of each
store will improve its performance.
Creating a number of smaller deduplication stores rather than one large store which receives data
from multiple backup hosts can have an impact on the overall effectiveness of deduplication. However,
generally the cross server deduplication effect is quite low unless you are storing a lot of common
data. If you store a large amount of common data on two servers, HP recommends that you back
these up to the same virtual library.

Optimizing Rotation Scheme to Reduce Housekeeping

Reducing the frequency of full backup cartridge reduces the amount of deduplication housekeeping
overhead required. You can optimize it using the following:
• Longer retention policy: Deduplication has little penalty for using a large number of virtual cartridges
in a rotation scheme and therefore a long retention policy for cartridges (most data will be the
same between backups and therefore deduplicated), which reduces the number of overwrites.
• Full vs. incremental/differential backups: The requirement for full or incremental backups is based
on how often offsite copied of virtual cartridges are required and on speed of data recovery. If
regular physical media copies are required, the best approach is that these are full backups on
a single cartridge. Speed of data recovery is less of a concern with a virtual library than with
physical media. For example, if a server fails and needs to be fully recovered from backup, the
recovery will require the last full backup plus every incremental backup since (or the last differential
backup). Finding and loading multiple physical cartridges is time-consuming. However, with virtual
tape there is no need to find all of the pieces of media. Because the data is stored on disk, the
time to restore is lower due the ability to randomly seek more quickly within a backup and load
a second cartridge instantly.
HP StorageWorks VLS and D2D Solutions Guide 59