09012 VTOC Reorganization Recommended

Identifies when a VTOC's DSCBs are not localized at the front of the VTOC.
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FILE: VOA Volume Allocation File SAS FILE NAME: DETAIL.VCAVOA01 SOURCE LOCATION: prefix.MICS.USER.SOURCE(DYVCAEXC) SEVERITY: Warning (SEVERITY='W') MANAGEMENT AREA: Performance (MGMTAREA='PERFORMANCE') PURPOSE: Identifies when a VTOC's DSCBs are not localized at the front of the VTOC. RATIONALE: VTOC search lengths are dependent on a DSCB Format 1 "highwater mark" that is maintained in the Format 4 DSCB. If the used DSCBs have become spread out within the VTOC, the search lengths can increase significantly, which results in poor performance. This spreading effect becomes a problem only when a large amount of VTOC space is in use. DEFINITION: This exception is based on the number of DSCBs that the Collector scanned to read all of the used DSCBs. This value divided by the number of used DSCBs is a good indication of how spread out the used DSCBs are. A further check is made to see what percent of VTOC DSCBs are in use. EXCEPTION STATEMENTS: The SAS statements identifying the exception situation and describing the condition are stored in the source member named in SOURCE LOCATION and are described below: /*---------------------------------------------------------*/ /* */ /* 09012 */ /* VTOC REORGANIZATION RECOMMENDED */ /* */ /*---------------------------------------------------------*/ IF DSCBU AND VOAINDXD NE 'Y' THEN DO; SPREAD=VOADSCBR/DSCBU; PCVTU =DSCBU/VOADSCBS; IF SPREAD GE #spread PCVTU GE #pcvtu THEN DO; EXCCODE='09012'; SEVERITY='W'; MGMTAREA='PERFORMANCE'; EXCDESC1='VTOC REORGANIZATION RECOMMENDED'; EXCDESC2='VTOC SPREAD INDEX=' || PUT(SPREAD,3.1) || ', VOL=' || VOLSER; LINK HIT; END; END; THRESHOLD MODIFICATION: The user should modify the #spread and #pcvtu values according to the following conventions: #spread - The maximum acceptable spread index value for DSCBs within the VTOC. A value of 2 means that the usable VTOC is twice as large as it needs to be (i.e., every other DSCB is a free DSCB). A value of 2 would be specified as: IF SPREAD GE 2 #pcvtu - The minimum percent of the VTOC in use. Spread indices will not be checked for VTOCs whose percent of space used is below this value. The value is the percent of VTOC DSCBs that are in use. A value of 25 percent would be specified as: IF PCVTU GE 25