IBM Tape Library Magstar 3494, Operator'S Manual

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VTS Active Data
The Active Data window (Figure 71) displays a graph showing the amount of active
data, amount of free storage, maximum active data, and a free storage alarm level
for the stacked volumes in a VTS. The data stored on stacked volumes is from the
Tape Volume Cache and may be compressed when the VTS has the EHPO feature;
therefore, the graphs do not represent actual host data bytes, but the compressed
volume sizes as stored in the Tape Volume Cache. A separate graph is available for
each VTS in the library. Data is displayed for the previous 29 days as of midnight
and for the current day on an hourly snapshot.
Active Data is the total size, as stored in the Tape Volume Cache, of all active
logical volumes that have been copied to stacked volumes. Virtual volumes that
exist in the Tape Volume Cache but have not been copied to tape are not included.
Invalidated (non-active) copies of logical volumes are also not included in the graph.
Maximum Active Data
is the total capacity of all stacked volumes that have been
inserted in the VTS. For the model B16, the Maximum Active Data is a theoretical
value computed by assuming that stacked volumes are filled with a 2:1
compression ratio. The model B18 uses the actual compression ratio achieved for
all data copied from the Tape Volume Cache to full stacked volumes to calculate the
Maximum Active Data. Because data received from enhanced ESCON host
attachments has previously been compressed into the Tape Volume Cache,
compression to the stacked volume from the Tape Volume Cache will be
approximately 1 to 1 for the B18. Note that invalidated copies of logical volumes
reduce the amount of active data you can store on the stacked volumes.
Figure 71. VTS Active Data Pop-Up Window
Chapter 6. Advanced Operating Procedures
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