Setting on compress for dumps and ABARS

A patch can be applied to specify that volume dumps are to be performed with the COMPRESS parameter. The advantage of compressing data is that the dump usually requires fewer output tapes. There are, however, two points to consider before applying the patch: 1) performing the compress function during a volume dump requires more CPU time and probably more elapsed time, and 2) dump volumes created with the COMPRESS parameter cannot be restored with some levels of the stand-alone version of DFSMSdss.

Among the types of volumes that may need to be restored with a stand-alone version of DFSMSdss are IPL volumes. To allow users the ability to dump data volumes using the COMPRESS parameter and to dump IPL volumes without using the COMPRESS parameter, DFSMShsm dump classes can be selected to suppress the COMPRESS parameter. Dumps made from the selected dump classes will not be compressed.

To specify that volume dumps be performed with the COMPRESS function, enter the PATCH command as follows:

PATCH .MCVT.+3C3 BITS(..1.....) /* use DFSMSdss COMPRESS for dumps */

Note:

If DFSMShsm is running with a release of DFSMSdss where COMPRESS and OPTIMIZE are mutually exclusive parameters of the DFSMSdss DUMP command, and if a dump is made using the COMPRESS parameter, DFSMShsm overrides the OPTIMIZE value specified by the SETSYS DUMPIO parameter.
The patch to use DFSMSdss COMPRESS for dumps also applies to ABARS when performing logical data set dumps during aggregate backup. If ABARS is running with a release of DFSMSdss where COMPRESS and OPTIMIZE are mutually exclusive parameters, the dump is made using the COMPRESS option. Otherwise, the dump is invoked using both OPTIMIZE and COMPRESS.
If the HWCOMPRESS keyword is specified for this dump through its dump class, the patch to use COMPRESS is ignored.
If the ZCOMPRESS keyword is specified for this dump through its dump class, and the patch to use COMPRESS is specified, then DFSMShsm specifies both the ZCOMPRESS(PREFERRED) and the COMPRESS keywords in the DFSMSdss DUMP command. If zEDC hardware is available, the dump is invoked using the ZCOMPRESS function. In case of a zEDC hardware failure, the dump is invoked using the COMPRESS function.

To specify that COMPRESS not be used for a certain dump class requires a patch to the dump class record at offset X'01'. The patch is required only if the DFSMShsm default has been changed to invoke COMPRESS during volume dumps. This CDS record change remains in effect until changed by a subsequent FIXCDS PATCH command, and it does not have to become part of a startup member. For more information on the FIXCDS command, see z/OS DFSMShsm Diagnosis.

In the following example the dump class IPLVOLS is being patched to suppress the COMPRESS parameter:

FIXCDS W IPLVOLS PATCH(X'01' BITS(1.......)) /* dump without compress.*/

Note: If a volume is dumped to multiple dump classes concurrently and any of the dump classes specify that the COMPRESS parameter is not to be used, then COMPRESS will not be used. No dumps from that dump generation will be compressed.

To determine whether a particular dump generation was made with or without COMPRESS, use FIXCDS DISPLAY to display its dump generation (DGN or G) record. If the X'04' bit in the 1-byte field at displacement X'00' in the variable portion of the record is on (the bit is set to 1), the dump was made with COMPRESS. The following example requests that the G record be displayed for the dump generation made from a source volume with serial number ESARES at 15.78 seconds past 1:44 p.m. on day 325 of year 1989:

FIXCDS G X'C5E2C1D9C5E2134415780089325F'

If the exact time the dump generation was made is not known, you may want to use the AMS PRINT command to print all the G records for dump generations of the volume in question directly from the BCDS. If the BCDS data set (cluster) name is DFHSM.BCDS, the following commands can be used under TSO to display the G records for the volume with serial number ESARES:

ALLOC DA('DFHSM.BCDS') FILE(BCDS) SHR
PRINT IFILE(BCDS) FKEY(X'29C5E2C1D9C5E2') TOKEY(X'29C5E2C1D9C5E2')

If this is done, the displacement to the field to be examined is X'40', not X'00'