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5 Automigration
In addition to copying virtual media to physical media via the backup application, another option
is to use automigration to perform transparent tape migration. The automigration feature allows
the VLS to act as a tape copy engine that transfers data from virtual cartridges on disk to a physical
tape library connected to the VLS device. Echo copy is the supported VLS automigration scheme.
NOTE:
When using automigration, virtual cartridge sizes are limited to 300 GB maximum when
deduplication is enabled. If you have LTO3/4/5 physical cartridges in the destination library, you
cannot size the virtual cartridges to be the same as the physical cartridges and therefore you cannot
utilize the full capacity of the physical tapes. If you create an automigration echo copy pool after
deduplication is enabled, it sets the copy pool policy to a default limit of 200 GB per virtual
cartridge; if you have an existing automigration echo copy pool when you enable deduplication,
you must set this maximum cartridge value in the copy pool policy.
Echo Copy Concepts
Echo copy essentially acts as a transparent disk cache to the physical library, so that echo copy
jobs can be performed at times other than the peak backup window. Once automigration is set
up, echo copy operations are automatic and seamless to the user. During the normal backup
window, the backup application writes to virtual cartridges. Each virtual cartridge that pertains to
an echo copy pool has header information that matches a physical cartridge in the tape library.
During the user-established automigration window, data migrates from each virtual cartridges to
its matching physical cartridge.
Echo copy is managed through the automigration software, not the backup application. For that
reason:
The destination library is not visible to the backup application, so it does not need licensing.
Copy traffic is no longer routed through the SAN.
Maximizes performance of high-speed tape drives by freeing bandwidth during the normal
backup window.
All destination tapes created by echo copy are in the native tape format, so they can be
restored directly from any tape drive or library that is visible to the backup application.
When determining whether to use echo copy, remember:
The destination library can only be used for copy operations.
Echo copy is a full tape copy, rather than an incremental change copy, so it can be an
inefficient use of media if you are using non-appending media pools in your backup jobs.
Human error is a factor to keep in mind. With linked media management, any mistakes with
the destination library's media will also affect the virtual cartridges. For example, if new tapes
are not loaded into the destination library, new, matching virtual tapes will not be created.
Subsequent backups will fail because the virtual tapes present are protected.
The backup application will not be aware of any copy failures.
Implementation
Echo Copy Pools
An echo copy pool is used to define which destination library slots are to be echoed by a specified
virtual library. Automigration then monitors the echo copy pool slots to detect cartridge loads and
ejects in the destination library. Automigration automatically synchronizes the virtual cartridges to
the destination cartridges, creating matching virtual cartridges as needed. When new destination
tapes are loaded, automigration scans them, and reads the backup application headers. It then
Echo Copy Concepts
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