2. PLANNING › 2.5 Special Considerations › 2.5.4 DASD Reserve Considerations

2.5.4 DASD Reserve Considerations

If SERIALIZE=N is specified as a run-time parameter, or is
defaulted by the omission of the keyword SERIALIZE, then VCC
will not ENQ on the SYSVTOC resource and will not RESERVE the
volume as the VTOC is being read.  When running VCC with
SERIALIZE=N, there is a small possibility that the VTOC might
be updated by SCRATCH, ALLOCATE, EXTEND, RENAME, or
PARTIAL-RELEASE processes; this chance is very small because
VCC reads an entire track of DSCBs with one I/O operation.
Many large enterprises run the production VCC scanning job
with SERIALIZE=N to eliminate the possibility of ENQ/RESERVE
problems.

If absolute data integrity is necessary, then SERIALIZE=Y
must be specified to cause VCC to issue an ENQ on SYSVTOC
which results in a RESERVE on the volume.  This serialization
is released as soon as "logical end-of-VTOC" is reached;
normally, this ranges from less than a second to a few
seconds depending on many variables.

The remainder of this section describes a series of
supplemental parameters that moderate the effect of
SERIALIZE=Y.

    o  The BYPASSRES option allows the specification of DASD
       volume serial numbers that will be processed without
       being reserved first.  To reduce the amount of keying
       required, generic values (prefixes) may be specified.

    o  The RESRETRY option allows you to specify the number
       of times VCC should attempt to reserve a volume.  Each
       attempt actually consists of three reserves, issued
       one second apart.  If the volume still cannot be
       reserved and the RESRETRY limit has not been exceeded,
       the volume will be placed back on the processing queue
       and will be tried again later.  When the RESRETRY
       limit is exceeded, the action taken depends on the
       value of the RESFAILOK option.

    o  The RESFAILOK option allows you to specify the action
       to be taken when a volume cannot be reserved.  Two
       options are available:  the volume can be processed
       without being reserved (message VCCVT21W will be
       issued), or processing for the volume can be
       terminated (message VCCVT22W will be issued).

Section 3.1.1.2 of this guide provides details about these
options.