APAR status
Closed as canceled.
Error description
Last Updated: 96/07/16 The information in this APAR is being provided to assist those customers interested in implementing access method (SAM/VSAM) Data Compression with DFSMSMVS. It also contains information which is of interest to those who have already implemented DFSMS data compression. The material is divided into: + General DFSMS/MVS compression information + Topic material on compression and related function The topics are organized in these general areas: + SAM compression and related functions + VSAM compression and related functions + System-managed volume selection + Data movement, including DFSMSdss + Considerations for IBM products using SAM/VSAM data sets ================================================================ = General DFSMS/MVS Compression Information = ================================================================ - II08685 contains the maintenance list which envelopes the fixes for all known DFSMS compression related problems. IBM STRONGLY RECOMMENDS that ALL maintenance listed in II08685 be APPLYed before implementing DFSMS compression. If additional PTFs are added to II08685 after implementing DFSMS compression, the additional PTFs should be APPLYed as soon as possible. - The following two publications contain general information for those interested in implementing DFSMS Data Compression. In addition, they identify a list of known restrictions and incompatibilities for data sets created in the compressed format, along with a discussion on performance. GG24-4056 DFSMS/MVS V1R2 Compression GG24-4251 DFSMS/MVS V1R2 Data Compression Impl. Guide - See APAR OW04773 for a description of the Compression Services reason codes returned with message IGD17162I (compression request not honored because data set characteristics do not meet compression criteria). ================================================================ = Topical Discussion = ================================================================ Each of the topic areas are organized into the following categories (if information for a category exists for the area): - general discussion material - recommendations and actions - additional information sources ***************************************** * SAM compression and related functions * ***************************************** ADDITIONAL INFORMATION SOURCES - OW08425 - Includes a documentation change which describes a list of return and reason codes which may appear in message ADR910E. - OW12009 - Describes a change in externals for AMS REPRO in regards to compressed format data sets. - OW11761 - Describes SAM Block Level Compression Enhancement. ****************************************** * VSAM compression and related functions * ****************************************** GENERAL DISCUSSION - VSAM does support locate mode (RPL OPTCD=LOC) for compressed data sets to permit compatible processing of existing programs. However, LOC mode processing is discouraged for several reasons: + A storage area must be obtained for each string, and at least one SVC must be issued to obtain the storage. Cross memory mode would not be allowed for the request. + The storage area needed may be of considerable size (up to 32K), and the number of areas needed may be as high as 255 for each ACB or resource pool. - VSAM OPEN does not allow the data component of a compressed data set to be opened separately. Access to a compressed data set is at the cluster level only. IDCAMS PRINT of the data component of a compressed data set is not allowed. - The VSAM Record Management trace facility is used to record VSAM control blocks while VSAM is processing. Tracing of the CPA and IOSB control blocks is not allowed for extended format data sets. Any request for these control blocks with extended format or compressed data sets is ignored. - To request data in extended format, the DSNTYPE=EXTENDED parameter must be coded in the assigned DATA CLASS. Two options exist on this parameter, REQUIRED|PREFERRED. The PREFERRED option is NOT supported for VSAM in DFSMS 1.2.0. If DSNTYPE=EXTENDED is coded for a VSAM data set, the allocation will fail if the extended format requirements cannot be met. The PREFERRED option IS supported for VSAM in DFSMS 1.3.0. If the extended format requirements cannot be met, a non-extended format allocation will be tried. - The EXCP counter in SMF type 30 records (SMF30BLK) for VSAM data sets in extended format has been changed to counting I/O requests, as opposed to blocks transferred. This makes it consistent with VSAM data sets not in extended format. - The storage abend described in documentation APAR OW21272 is more likely to surface with a compressed VSAM data set than a non-compressed data set, assuming the application uses unique tasks for CLOSE and GET/PUT processing without sharing subpool 0. See APAR OW21272 for more details. (96/07/16 tly) ADDITIONAL INFORMATION SOURCES - See apar OW11649 for a discussion on SMF30BLK counts for VSAM extended format data sets. - See apar OW01740 for general information concerning VSAM partial release. *********************************** * System-managed volume selection * *********************************** GENERAL DISCUSSION - There are two volume selection paths in DFSMS/MVS. One path is referred to as the general volume selection path, the other is the striped volume selection path. VSAM data requested in extended format, required for data compression, follows the general path. SAM data in extended format, also required for data compression, follows the striped path. This design is enhanced via APAR OW12656 (PTF UW18842) in DFSMS 1.2 and is included in DFSMS 1.3. UW18842 is enclosed in the envelope of PTFs listed in II08685. - Until the maintenance for APAR OW12656, as discussed in the referenced WSC Flash below, is available, users may experience failures in allocating a data set as extended format due to volumes exceeding high threshold. They will also lose the concept of an "overflow" pool. These will both be addressed with that maintenance for APAR OW12656. If a SUSTAINED DATA RATE greater than 0 (zero) is specified, SMS will still use the striped volume selection path and enforce the below high threshold, non-quiesce, and other stripping rules which apply to striping (even if OW12656 is applied). - After installing the maintenance for OW12656, there is a user consideration relative to the use of guaranteed space. If guaranteed space is specified and STORAGE CLASS parameter SUSTAINED DATA RATE ^= 0|blank, and the stripe count cannot be met with the available volumes, the space quantity will be adjusted based on available volume count. If SUSTAINED DATA RATE = 0|blank, the user specified space quantity must be available on all volumes, based on user specified volume count. - It should be emphasized that for Sustained Data Rate (SDR)= 0|blank, a single-stripe data set will be allocated, regard- less of whether guaranteed was specified or not. For example, if the STORAGE CLASS specifies SDR=0 Guaranteed Space and a volume count of three is specified, SMS will allocate a single-stripe, three volume data set. RECOMMENDATIONS AND ACTIONS - DFSMS 1.2 APAR OW13048 (UW18900) and APAR OW13030 (UW18816) should be installed along with APAR OW12656 (UW18842) for full function capability. UW18900, UW18816, and UW18842 are enclosed in the envelope of PTFs listed in II08685. ADDITIONAL INFORMATION SOURCES - WSC Flash 9517 - addresses the issues of volume selection for SAM data in extended format. - WSC Flash 9515 - hardware requirements for data in extended format, including 3990-3 parallel channel support. - II07464 - information related to rejecting a volume during the selection process. - II08442 - discussion related to system-managed storage and Dynamic Cache Management Enhanced (DCME). ************************************* * Data movement, including DFSMSdss * ************************************* GENERAL DISCUSSION - Support for conversion from extended sequential to non- extended sequential during copy or restore processing is limited to Storage Controllers that support Extended Count Key Data ( ECKD ); specifically the Define Extent and Locate Record Channel Program commands ADDITIONAL INFORMATION SOURCES - Documentation APAR OW10518 states that DFSMSdss cannot support dumping to a compressed extended sequential data set during a DFSMSdss DUMP operation. - WSC Flash 9526 - Discusses the implications of implementing SAM Compression without DFSMSdss APAR OW12062 applied - II08303 contains information related to DFSMSsdm and the Remote Copy function ( XRC / PPRC ). Two of the PTFs in the MAINTENANCE RECOMMENDATION section above for DFSMSsdm are for the Remote Copy support. Please see this information APAR for additional considerations and recommended maintenance when the Remote Copy support is installed. *********************************************************** * Considerations for other IBM Products using Compression * *********************************************************** GENERAL DISCUSSION - IMS IMS cannot process data sets in a compressed format. This includes IMS logs and image copies - DB2 DB2 archive log data sets should NOT be defined as extended format data sets. DB2 uses BDAM to access the data sets - CICS It is STRONGLY suggested that DFHDMPA, DFHDMPB, DFHJ0xx, DFHINTRA, and DFHTEMP are NOT defined as extended format data sets. These data sets should not be compressed for any reason. RECOMMENDATIONS AND ACTIONS - ISPF Apply the applicable ISPF maintenance listed below for processing extended format data sets with ISPF ISPF 3.5 ISPF 4.1 ISPF 4.2 OW11950/UW19195 OW12712/UW17165 OW15163/UW20916 OW12084/UW16846 OW13310/UW18840 OW16099/UW22220 OW16995/UW24006 OW13811/UW18881 OW16099/UW22219 - C370 Using fopen(rb,type=record) with a concatenation of datasets which includes a DFSMS compressed file may not read all of the datasets. See C APAR PN83962 for fix information. ADDITIONAL INFORMATION SOURCES - DFSMS/MVS Version 1 Release 2.0 Compression (Red Book) GG24-4056-00 Chapter 4, pg.77 states; "You must not define a data class with Compaction=Y for IMS data sets. IMS fails the OPEN, if it finds that DFSMS/MVS facilities have compressed ANY of its data sets." - II08608 - Discussion of system-managed storage and CICS system data sets. - II06249 - Discussion of errors that may occur if DB2 archive log data sets are compressed ================================================================ ADDITIONAL KEYWORDS: compressed compress extended comprs V1R2 1.2 R1B0 V1R3 1.3 R1C0
Local fix
Problem summary
Problem conclusion
Temporary fix
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APAR Information
APAR number
II08631
Reported component name
V2 LIB INFO ITE
Reported component ID
INFOV2LIB
Reported release
001
Status
CLOSED CAN
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
1995-04-24
Closed date
1997-11-07
Last modified date
1997-11-07
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
Fix information
Applicable component levels
[{"Business Unit":{"code":"BU054","label":"Systems w\/TPS"},"Product":{"code":"SG19M","label":"APARs - z\/OS environment"},"Platform":[{"code":"PF054","label":"z\/OS"}],"Version":"001"}]
Document Information
Modified date:
09 September 2020