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

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– Release <strong>of</strong> unused, over-allocated space<br />

– Migration to DFSMShsm-owned migration level 1 (ML1) volumes (compressed)<br />

► Automatic secondary space management <strong>of</strong> DFSMShsm-owned volumes, which includes:<br />

– Migration-level cleanup, including deletion <strong>of</strong> expired migrated data sets and migration<br />

control data set (MCDS) records<br />

– Moving migration copies from migration level 1 (ML1) to migration level 2 (ML2)<br />

volumes<br />

► Automatic interval migration, initiated when a DFSMShsm-managed volume exceeds a<br />

specified threshold<br />

► Automatic recall <strong>of</strong> user data sets back to DASD volumes, when referenced by the<br />

application<br />

► Space management by command<br />

► Space-saving functions, which include:<br />

– Data compaction and data compression. Compaction provides space savings through<br />

fewer gaps and less control data. Compression provides a more compact way to store<br />

data.<br />

– Partitioned data set (PDS) free space compression.<br />

– Small data set packing (SDSP) data set facility, which allows small data sets to be<br />

packaged in just one physical track.<br />

– Data set reblocking.<br />

It is possible to have more than one z/<strong>OS</strong> image sharing the same DFSMShsm policy. In this<br />

case one <strong>of</strong> the DFSMShsm images is the primary host and the others are secondary. The<br />

primary HSM host is identified by H<strong>OS</strong>T= in the HSM startup and is responsible for:<br />

► Hourly space checks<br />

► During auto backup: CDS backup, backup <strong>of</strong> ML1 data sets to tape<br />

► During auto dump: Expiration <strong>of</strong> dump copies and deletion <strong>of</strong> excess dump VTOC copy<br />

data sets<br />

► During secondary space management (SSM): Cleanup <strong>of</strong> MCDS, migration volumes, and<br />

L1-to-L2 migration<br />

If you are running your z/<strong>OS</strong> HSM images in sysplex (parallel or basic), you can use<br />

secondary host promotion to allow a secondary image to assume the primary image's tasks if<br />

the primary host fails. Secondary host promotion uses XCF status monitoring to execute the<br />

promotion. To indicate a system as a candidate, issue:<br />

SETSYS PRIMARYH<strong>OS</strong>T(YES)<br />

and<br />

SSM(YES)<br />

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

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