Sizing The Tape Library; Shared Virtual Library - HP StorageWorks 12000 - Virtual Library System EVA Gateway Manual

Figure 64 Shared Virtual Library
.
In this scenario, there is one or more physical tape libraries that need to be mapped to a single,
shared virtual library. The physical library or libraries can be bigger or smaller than the available
disk space on the virtual library. If the physical library has more capacity than the available disk of
the virtual library, only a subset of its slot range is assigned to the virtual library. This allows multiple
backup servers to backup to the shared virtual library, and then during the copy window, all the
virtual cartridges from the virtual library are automatically and transparently copied to the one or
more physical tape libraries mapped to that virtual library. This scheme therefore provides daily off-site
protection of the physical tapes.
The ability to map multiple physical tape libraries to a single virtual library means that customers can
start with smaller, single physical libraries. As they upgrade the capacity of their virtual libraries,
customers can add additional physical libraries without needing to modify their backup jobs.
The user can configure additional virtual slots in the virtual libraries. That is, there can be more virtual
slots than the number of physical slots mapped to the virtual library, to provide spare slots for restore
from disk. These additional slots in the virtual library can also be used to contain purely virtual media
(for example, media that has no mapping to any physical tape). The user can then create a separate
media pool for the purely virtual cartridges, so that not all backups go to physical tape. For example,
the user can direct full backups to the media pool containing the automigration virtual cartridges, and
incremental backups to the purely virtual media. Thus, only full backups are going to physical tape.
An alternative to this would be to create a separate virtual library for incremental backups which
would contain purely virtual cartridges.

Sizing the Tape Library

When sizing the physical tape library (or library partition) for use with automigration, the number of
tape drives should be selected depending on the required copy performance. A single automigration
copy stream runs at 100-120 MB/sec, so six copy streams per node will saturate the node at 600
MB/second aggregate copy performance. Maximum copy performance would therefore be achieved
using six LTO3 or LTO4 tape drives per node (or ten LTO2 tape drives) multiplied by the number of
HP StorageWorks VLS and D2D Solutions Guide 147