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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- 1 20 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 nodes in the VLS. If the copy window does not need maximum copy
performance, you can use even fewer tape drives per node.
For example, a 4-node VLS9000 device that needs to automigrate 64 TB every night within an
eight hour copy window (that runs after the backups are complete) requires an aggregate copy
performance of 2200 MB/sec. With a 100- 1 20 MB/sec per copy stream, this implies a tape
library would need 18-22 LTO3/LTO4 tape drives to achieve this copy performance. Remember
these tape drives should be evenly spread across both back-end Fibre Channel ports of every VLS
node. In other words, half the drives should be connected to the first back-end Fibre Channel port
on every node, and the other half should be presented to the second back-end Fibre Channel port
on every node.
Restoring from Automigration Media
When using automigration to create physical backups, if the destination tape is still loaded in the
destination library, its matching virtual cartridge will still be present in the virtual library. In this
case, the user can simply restore from the virtual cartridge using the backup application.
If the destination tape has been ejected from the destination library, the user has the following
options:
1.
If the automigration virtual cartridge still exists in the firesafe (for example, if the policy-defined
retention period has not expired), use Command View VLS to manually move the cartridge
back into the virtual library. You can then restore from the virtual cartridge using the backup
application, and then move the cartridge back to the firesafe.
2.
If the automigration virtual cartridge has been deleted from the firesafe, retrieve the physical
cartridge by one of the following methods:
Load the physical cartridge into any compatible physical drive or library that is visible to
the backup application and restore from that tape using the backup application.
Load the physical cartridge into the destination library and use Command View VLS to
perform a Load Media for Restore, which copies the entire destination tape back into a
virtual cartridge. You can then restore from the virtual cartridge using the backup
application. The Load Media for Restore process always creates a whole cartridge
(non-deduplicated) copy even if deduplication is enabled. However, because deduplication
allows you to increase the amount of time to retain virtual cartridges in the Firesafe,
restoring from physical tape should be an infrequent event.
Restoring from Automigration Media
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