Blocksize And Transfer Size; Lan-Free Backups; Retention Planning - HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual

NetBackup, etc.) support dual paths to the library change device and will automatically switch over
to the alternate path if the primary path fails.
Multipathing virtual tape drives is not recommended. Many enterprise backup environments (operating
systems or backup application) do not support dual path to tape drives because they see this as two
separate drives. Given the fact that a virtual library can create many virtual tape drives over multiple
different Fibre Channel ports, if a SAN fabric fails (and you have a dual-path changer configured)
the only impact of this is that half the virtual tape drives cannot be accessed but the remaining half
of the drives in the library can still be used and can still access every virtual cartridge in the library.
This also implies that when a SAN fabric fails this halves the available Fibre Channel performance
so if full backup performance is required even after a SAN fabric failure then the VLS needs to be
configured with double the number of Fibre Channel ports. Instead of configuring dual path virtual
tape drives, it is better to configure single-path virtual tapes across multiple Fibre Channel ports that
are connected to both SAN fabrics.
NOTE:
The D2D can configure its two LAN ports in high availability port mode (see
this is transparent to the backup application because it only sees one "bonded" path to the virtual
library.

Blocksize and Transfer Size

As with physical tape, larger tape block sizes and host transfer sizes are of benefit; they reduce the
amount of overhead of headers added by the backup application and the transport interface.
• D2D: HP recommends a minimum of 64 KB blocksize and suggests up to 1 MB.
• VLS: HP recommends a blocksize of 256 KB (the maximum supported).

LAN-free Backups

All enterprise backup applications provide the ability to run "LAN-free" backups. This is where
application servers connected to the SAN run the backup media agent and can perform backups
directly over the SAN to the tape library. This removes this backup traffic from the LAN and speeds
up backups (by removing the LAN performance bottleneck). One of the disadvantages of LAN-free
backup to a physical library is that it cannot be multiplexed because each backup stream is written
directly from the data source to the tape drive, and so it could generally only be used with the largest
application servers which can supply high speed backup streams.
One of the key advantages of a SAN virtual library is the ability to increase the amount of LAN-free
backup used. With a virtual library you do not have to provide maximum performance per LAN-free
backup stream as needed on physical tape drives. You can create many virtual drives and thus enable
LAN-free backup on any SAN-connected appliance servers (regardless of their performance) that are
large enough to bother with LAN-free backup. This improves the backup performance of the LAN-free
backups and also improves performance of the remaining LAN backups because the LAN-free backup
traffic has been removed from the LAN.

Retention Planning

Retention planning and sizing go hand in hand. How long do you need to keep data on disk? How
many full backups do you want to keep on disk? How many incremental backups? How do you want
HP StorageWorks VLS and D2D Solutions Guide
D2D Ethernet Ports), but
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