PDS Compression › JCL — PDS Compression › SCAN Command

SCAN Command

The SCAN command can be used to select one or several datasets for compression from one or more volumes.

During SCAN processing, datasets that are eligible for compression, but which are in use by other tasks, are noted and bypassed until the end of processing for that volume. At that time, the compress procedure re-examines the bypassed datasets to see if they are still in use by other tasks. If not, they are processed. For those datasets still in use, CA Disk issues an informational message and no processing is performed.

Note: SMS managed datasets that are not cataloged will only be processed when the USE parameter is specified. Otherwise, the data set will be bypassed.

The parameters described below specify the selection criteria as well as the reallocation values.

The SCAN command syntax is:

SCANSIMULATE,VOLUMES=,EXTABLE=,DSNAMES=,THRESHOLD=,EMPTY,USE,SHRINK,CONVERT,

ALLOCATE=,RESERVE,PASSWORD

SIMULATE

This parameter causes the output report to be produced as if compression had been performed. However no actual compression occurs.

Note: SIMULATE has the following implications:

• Since data integrity is not an issue during SIMULATE processing, no ENQ or RESERVES are performed. This eliminates system contention for datasets and enhances performance.
• Sysparm ENQDSSIM can be specified with a value of Y to cause ENQUEUEs to be issued. For further details, see the sysparm description for ENQDSSIMn in the Systems Guide.
• The directory is always read, whether you specify SIMULATE or not.
• CA Allocate, SMS, or other allocation products can override the actual allocation. So the selected data sets will not be compressed as indicated.
• Smaller empty PDSs can be selected for compression, but not actually changed because of minimum directory requirements.

To further enhance performance during SIMULATE processing, only the count fields of the member data blocks are read, which provides sufficient information to calculate reallocation values.

VOLUMES=

A list of one or more volumes or volume prefixes must be specified to designate the volumes to be scanned for PDS datasets to be compressed. Default processing looks for these volumes only as online real disk packs. (A maximum of 50 entries is supported.)

EXTABLE=

Specify for this parameter the name of the parmlib member that contains entries consisting of either complete data set names or patterns that are to be excluded from compression. This parameter can be nullified during SIMULATE runs by specifying sysparm PDSEXSIM with a value of N. This allows even the excluded datasets to be reported on during SIMULATE runs, although live runs will exclude them.

DSNAMES=

Candidates for compression can be restricted to those datasets having names or pattern names that are specified in the list value of this optional parameter. (A maximum of 10 entries is supported.)

THRESHOLD=

This parameter provides a method of limiting those datasets selected for compression. It allows you to define five conditions, one of which must be met before a PDS will be eligible for processing. Datasets can be selected based on threshold ceilings, so you can recover dead space and/or increase allocation amounts to reduce out of space problems. Datasets can also be selected based on threshold floors, so you can recover overallocated space. (This parameter applies only to PDSs containing members. See EMPTY For a similar test for PDSs containing no members.)

The conditions have the following format and meaning: (UC,XC,DC,UF,DF)

• UC Used Ceiling — The maximum percentage of allocated space (excluding the space allocated to the directory blocks) that is used. This value can be thought of as a ceiling to the threshold range. Any data set using more than this percentage of allocated space will be eligible for processing. A value of 0 will nullify this threshold test.
• XC Extent Ceiling — The maximum number of extents used by each data set. This can be thought of as a threshold ceiling. Any data set going into more than this number of extents will be eligible for processing. A value of 0 will nullify this threshold test.
• DC Directory Ceiling — The maximum percentage of directory space that is used. This can be thought of as a ceiling to the threshold range. Any data set that has a directory using more than this percentage of allocated directory space will be eligible for processing. A value of 0 will nullify this threshold test.
• UF Used Floor — The minimum percentage of allocated space (excluding the space allocated to the directory blocks) that is used. This value can be thought of as a floor to the threshold range. Any data set using less than this percentage of allocated space will be eligible for processing. A value of 0 will nullify this threshold test.
• DF - Directory Floor — The minimum percentage of directory space that is used. This value can be thought of as a floor to the threshold range. Any data set that has a directory using less than this percentage of allocated directory space will be eligible for processing. A value of 0 will nullify this threshold test.

THRESHOLD= (continued)

For conditions UC and DC, specifying a value of 100 or more will cause all datasets to fail the threshold ceiling test. For condition XC, specifying a value of 16 or more will cause all datasets to fail the threshold ceiling test.

Since these thresholds provide the upper and lower limits for datasets that are considered ineligible for processing, it is not valid to specify for conditions UF and DF a value higher than the value specified in conditions UC and DC, respectively.

See also the USE, SHRINK and CONVERT parameters for how they are used in conjunction with THRESHOLD=.

EMPTY

This parameter provides an additional method for selecting datasets for compression. By specifying EMPTY, you extend PDS Compress processing to include empty datasets (that is, PDSs containing no members).

• If this parameter is not present, empty datasets will not be selected for processing. However, in explicit mode (that is, the COMPRESS command) the SPACE= parameter will force the compress even if the data set is empty.
• If the EMPTY parameter is specified along with THRESHOLD=(0,16), only empty PDSs will be selected.
• Selected empty datasets are indicated by an EF in the THRESHOLD EXCEEDED field of the PDS Compression report.
• When the EMPTY parameter is specified, processing is affected by the USE parameter as follows:
• If the USE parameter is present, any dead space once used for members that have been deleted is eliminated.
• If the USE parameter is not present, all primary space (excluding the space required for the directory blocks) is freed. The space thus freed is divided by 15 (the number of possible secondary extents) and added to the current secondary allocation amount. This in effect compresses the data set down to its smallest amount while still allowing room for future expansion. See also the CONVERT and SHRINK parameters.
• When EMPTY is specified, the following conditions for compression can be displayed in the THRESHOLD EXCEEDED column of the compression report.
• EC Empty Ceiling -- This condition is triggered when the DS1LSTAR field of the Format-1 DSCB does not point to the first record after the directory. This can occur when all members have been deleted, and the data set has not yet been compressed.
• EF Empty Floor -- This condition is set for empty PDS's when EMPTY was specified on the command line and the USE parameter was not specified. The action is to free all space except that needed for the directory.
• Smaller, empty PDSs cannot be further compressed because of minimum directory requirements, CA Allocate, SMS, or other products that override allocation.

USE

The presence of this parameter forces the use of the existing data set extent(s). Any allocation changes, if specified, are confined to directory adjustment; that is, the PP and SS sub parameters of the ALLOCATE= parameter are ignored and only the DD readjustment is done.

• For empty datasets (if the EMPTY parameter is also specified), the presence of this parameter will cause the ALLOCATE= parameter to be ignored.
• If the USE parameter is present and sysparm PDSENQSH is specified with a value of Y, only a SHARED ENQ is maintained for the data set during compression. In addition, ISPF and linkage editor enqueues are issued to preserve the data set's integrity.

SHRINK

Specify this parameter to allow the data set allocation to be reduced. Default processing (this parameter absent) will not allow a data set to be reduced in size. The ALLOCATE= parameter must be present for SHRINK to be active.

Empty datasets (if the EMPTY parameter is also specified) will be reduced in size regardless of whether or not the SHRINK parameter is specified. Specifying the SHRINK parameter, however, provides an even greater space savings, because it reduces the directory allocation down to one track (or cylinder—see CONVERT parameter), thus permitting the primary space allocation to also be reduced to a single track (or cylinder).

CONVERT

This parameter can be used in conjunction with the SHRINK parameter for datasets currently allocated in cylinders. If it is specified on the same command as the USE parameter, CONVERT will be ignored. When a new space allocation is calculated and is less than one cylinder, this parameter converts the space allocation amount and type from cylinders to tracks (or blocks). This includes datasets allocated with the ROUND request in which the blocks are rounded up to space equal to an integral number of cylinders.

• For empty datasets (if the EMPTY parameter is also specified), the CONVERT parameter will have the following effect:
• If the SHRINK parameter is not present, the primary allocation will be reduced to the minimum number of tracks required to hold the directory blocks.
• If the SHRINK parameter is also specified, the primary allocation (including the directory blocks) will be reduced to one track.

ALLOCATE=

This optional parameter specifies three values used to reallocate the primary space, secondary space and directory space. The format and meanings are as follows:

(PP,SS,DD)

• PP—The percentage of primary space (excluding the space allocated to the directory blocks) to be used after reallocation and compression. A value of 0 can be used to force the new allocation equal to the original.
• SS—The new secondary allocation quantity (excluding the space allocated to the directory blocks) expressed as a percentage of the primary. A value of 0, which is the default, can be used to force the new allocation equal to the original.
• DD—The percentage of directory space to be used after reallocation and compression. A value of 0, which is the default, can be used to force the new allocation equal to the original.

See the USE, SHRINK and CONVERT parameters for how they are used in conjunction with ALLOCATE=. Also see the SPACE= parameter (described under the explicit COMPRESS command in the following section.)

RESERVE

This parameter is provided for use in a multiple- CPU environment that does not use a global enqueue facility, to protect against other CPUs making concurrent updates. It causes a RESERVE to be issued against the volume in addition to the shared or exclusive ENQ already issued on the data set name. (See USE.) If this parameter is omitted, only the ENQ is done. The RESERVE and/or ENQ are done just prior to the compress of each data set and DEQ is issued immediately upon completion.

PASSWORD

This parameter is active only if sysparm PASSWORD has been specified with a value of Y. Specify this parameter to allow CA Disk to compress password- protected datasets without prompting the operator for the password. If you do not specify this parameter, CA Disk will bypass these password-protected datasets.