IBM TotalStorage 3494 Tape Library, Operator'S Manual

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In setting up a PtP VTS and when using the delete expired volume data function,
the following considerations apply depending on the I/O selection mode of
operation.
v
For No Preference Ensure that the non-zero expire time on both library
managers is set to the same value. If not, the VTS that expires the data first will
not be used for scratch mounts.
v For Preferred VTS Ensure that a non-zero expire time is set on both library
managers and that the non-preferred VTS/Library is set to delete the data before
the preferred VTS/Library.
Setting a non-zero expire time on only the preferred library or setting it to delete
data before deletions on the non-preferred one can cause scratch mounts to use the
non-preferred VTS for I/O. It is recommended that the data on the non-preferred
VTS/Library be set to be expired a minimum of 48 hours ahead of the data on the
preferred VTS. An additional amount should be added to account for the amount
of time the VTSs are to be disconnected for a disaster recovery test. For example, if
the maximum disconnected time for a test is 24 hours, then the setting on the
preferred VTS/Library should be 72 hours more than the setting on the
non-preferred VTS/Library.
Selecting the Hold option on the Define Fast Ready Categories window (Figure 147
on page 244) prevents a logical volume from being selected for mount processing
or to be moved out of its assigned category until the expire time has elapsed or
has been reset to zero.
Scratch Stacked Volumes
It is essential that sufficient scratch stacked volumes be available for use by a VTS
for copying a virtual volume when the volume is closed. A warning is provided
when the Free Storage Threshold cannot be met with the scratch stacked volumes
that are available. See the VTS Management Policies window, shown in Figure 148
on page 245.
The Reclaim Threshold Percentage as entered in the VTS Management Policies
window becomes important when the supply of scratch stacked volumes is low.
The VTS Space Reclamation Algorithm may impact the VTS performance when it
is necessary to reclaim expired space on stacked volumes. A high Reclaim
Threshold Percentage requires that more active data be moved (using VTS
resources) to free the stacked volume for scratch use. As a general rule, you should
try not to exceed 30%–40% as a Reclaim Threshold Percentage. It is better to add
additional stacked volumes than to increase this value. When there are less than
ten scratch stacked volumes, the Inhibit Reclaim Schedule shown in the VTS
Management Policies window, Figure 148 on page 245, is not in effect, and the VTS
proceeds to reclaim space on stacked volumes until at least 15 scratch stacked
volumes are available. For the Inhibit Reclaim Schedule to be in effect with
non-invasive reclamation activity by the VTS, more than 50 scratch stacked
volumes must be available. Reclamation activity may affect the performance of the
host jobs that run on the VTS.
Integration with the 3494 Tape Library
A TS7700 Virtualization Engine or VTS must be associated with a 3494 Tape
Library because the physical assets used by the subsystem are managed by the
Library Manager in the 3494 Tape Library. The physical assets include the tape
drives and the cartridges that are used for stacking logical volumes. The Library
Manager provides several other key functions involving a VTS or TS7700
Virtualization Engine:
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3494 Tape Library Operator Guide