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ABCs of z/OS System Programming Volume 3 - IBM Redbooks

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4.48 VSAM enhancements<br />

Data compression for KSDS<br />

Extended addressability<br />

Record level sharing (RLS)<br />

<strong>System</strong>-managed buffering (SMB)<br />

Data striping and multi-layering<br />

DFSMS data set separation<br />

Free space release<br />

Figure 4-59 VSAM enhancements<br />

VSAM enhancements<br />

The following list presents the major VSAM enhancements since DFSMS V1R2. For the<br />

majority <strong>of</strong> these functions, extended format is a prerequisite. The enhancements are:<br />

► Data compression for KSDS - This is useful for improving I/O mainly for write-once,<br />

read-many clusters.<br />

► Extended addressability - This allows data components larger than 4 GB. The limitation<br />

was caused by an RBA field <strong>of</strong> 4 bytes; RBA now has an 8-byte length.<br />

► Record-level sharing (RLS) - This allows VSAM data sharing across z/<strong>OS</strong> systems in a<br />

Parallel Sysplex.<br />

► <strong>System</strong>-managed buffering (SMB) - This improves the performance <strong>of</strong> random NSR<br />

processing.<br />

► Data stripping and multi-layering - This improves sequential access performance due to<br />

parallel I/Os in several volumes (stripes).<br />

► DFSMS data set separation - This allows the allocation <strong>of</strong> clusters in distinct physical<br />

control units.<br />

► Free space release - As with non-VSAM data sets, the free space that is not used at the<br />

end <strong>of</strong> the data component can be released at deallocation.<br />

186 <strong>ABCs</strong> <strong>of</strong> z/<strong>OS</strong> <strong>System</strong> <strong>Programming</strong> <strong>Volume</strong> 3

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