Elastic Capacity - IBM TS4500 Introduction And Planning Manual

The TS4500 tape library supports media verification to verify that the data on your
media is readable. The verification process is controlled at the logical library level.
Media verification is set up to run automatically on a set date, but you can verify
individual cartridges before the set date. Logical libraries that use AME or SME
encryption cannot use media verification.
You can set the recurring schedule for media verification by day, months, or years.
Cartridges that are in the process of verification are still available for media access.
If the library receives a request for information on a cartridge that is being verified,
the verification is suspended and the cartridge is released to fill the request. When
the cartridge is no longer needed, verification is resumed.
The move and eject actions are disabled for cartridges in the verification process.
You have to first stops the verification process before you can move, or eject a
cartridge that are being verified.
Enabling Media Verification
The first step to using media verification is selecting at least one tape drive in your
library as a media verification drive. You should have at least two drives to ensure
that there are no false positives due to a faulty tape drive. Tapes that fail
verification are retried on the second drive, if available, before they are reported as
faulty.
Once you selected the verification drives, go to the Cartridges by Logical
Librariespage in the TS4500 tape library GUI. Right-click on the logical library to
enable media verification and set the verification schedule.
When media verification is enabled on a logical library for the first time, all the
cartridges become due for verification on the same date. The initial queue for
media verification might take up to several months to be established. This depends
on the number of cartridges, how full they are, and the number of media
verification drives. Once a cartridge is verified, the next verification date is based
on the time period set in the verification policy.

Elastic capacity

In a dual-accessor configuration, the TS4500 tape library contains limited access
columns that you can use for special situations. You can use these columns to store
least recently used data cartridges, or as a temporary overflow area. The use of the
limited access columns (Elastic Capacity) allows dual-accessor customers to achieve
the same storage capacity as if the library was single accessor.
Elastic Capacity Settings
Go to Settings > Library > Cartridges and Accessors in the TS4500 tape library
GUI to modify the Elastic Capacity settings. Choose one of the three options for
Elastic Capacity.
Use for maximum capacity
Use this setting to store media cartridges in the limited access (Elastic Capacity)
columns. When the dual-access area (the cartridge slots that both A and B
accessors can reach) exceeds the usage threshold, the least recently used cartridges
are move into the Elastic Capacity area. The default usage threshold is 98%.
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IBM TS4500: Introduction and Planning Guide