PL57283: D/T3480 D/T3490 TAPE IDRC RECOVERY PERFORMANCE DEGRADATION MSGIEC707I WARNING - RDBACK ON COMPACTED DATA

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• 3480 | 3490 TAPE UNITS WITH THE IDRC (Increased Data Recording
  Capability) COMPACTION FEATURE CANNOT READ COMPACTED DATA
  BACKWARD. IN ORDER TO SATISFY A READ BACKWARD REQUEST THE DRIVE
  MOVES THE TAPE BACKWARD ONE RECORD AND READS FORWARD ONE
  RECORD. THIS EXCESSIVE TAPE MOVEMENT CAUSES DB2 RECOVERY USING
  LOG DATA FROM CARTRIDGE TO SLOWDOWN CONSIDERABLY AND RESULTS
  IN A SEVERE PERFORMANCE DEGRADATION.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: ALL                                          *
  ****************************************************************
  * PROBLEM DESCRIPTION: D/T3480 IDRC RECOVERY PERFORMANCE       *
  *                      DEGRADATION.                            *
  ****************************************************************
  * RECOMMENDATION: INSTALL CORRECTIVE SERVICE FOR APAR/PTF      *
  ****************************************************************
     TAPEDRIVE UNITS WITH THE Improved Data Recording Capability
  (IDRC) COMPACTION FEATURE DO  NOT  PROVIDE THE ccwop 0C 'READ
  BACKWARD' FUNCTION WHICH ALLOWS A USER TO READ BACKWARDS
  THROUGH A TAPE. INSTEAD OF A 'READ BACKWARD' COMMAND, THE IDRC
  FEATURE TRANSLATES THIS COMMAND INTO A 'SET BACK ONE RECORD'
  AND A 'READ FORWARD ONE RECORD', WHICH IS VERY SLOW. FOR MOST
  JOBS DOING NORMAL TAPE I/O (E.G. FORWARD READS/WRITES), THIS
  IS NOT A PROBLEM. UNFORTUNATELY, DB2 READS BACKWARD
  EXTENSIVELY WHEN ACCESSING ARCHIVE LOG TAPES TO ROLL OUT A
  UNIT OF RECOVERY. THIS EXCESSIVE TAPE MOVEMENT CAUSES DB2
  RECOVERY USING LOG DATA FROM TAPES TO SLOW DOWN CONSIDERABLY.
  

Problem conclusion

•    THE CODE HAS BEEN CHANGED TO GIVE A DB2 USER THE OPTION OF
  WHETHER THE USER WANTS DATA COMPACTION OR NOT WHEN WRITING
  ARCHIVE LOGS TO D/T34x0 DEVICES. THIS OPTION WILL BE INVOKED
  AS A DSNZPARM ON THE DSNTIPA INSTALLATION PANEL AND BE
  CONTROLLED THROUGH THE USE OF THE DSN6ARVP MACRO. THIS ZPARM
  WILL ONLY AFFECT D/T34x0 DEVICES WITH THE IDRC FEATURE. THE
  DEFAULT WILL BE TO NOT COMPACT THE DATA. ACCORDINGLY, SECTION
  2, VOLUME 1, PLANNING AND INSTALLING DB2 OF THE DB2
  ADMINSTRATION GUIDE (SC26437401) WILL BE CHANGED AS FOLLOWS:
  A.THE FOLLOWING OPTION WILL BE ADDED TO FIGURE 31 OF PG. 2-107:
  
   14. COMPACT DATA    ===> NO    YES OR NO FOR DATA COMPACTION
  
  B. THE FOLLOWING DESCRIPTION OF DATA COMPACTION WILL BE ADDED
     TO PAGE 2-110:
  |+--------------------+----------------------------------------+
  || 14. COMPACT DATA   | DEFAULT: NO                            |
  || CLIST: ARCHCOMP    | ACCEPTABLE VALUES: YES, NO             |
  || DSNZPARM: DSN6ARVP |RUPDATE:OPTION 1(DSNTIPB),UPDATE DSNTIPA|
  |+--------------------+----------------------------------------+
  
  |SPECIFIES WHETHER OR NOT DATA WRITTEN TO ARCHIVE LOGS SHOULD
  |BE COMPACTED. THIS OPTION ONLY APPLIES TO DATA WRITTEN TO A
  |D/T34xx DEVICE THAT HAS THE NEW IMPROVED DATA RECORDING
  |CAPABILITY (IDRC) FEATURE. WITH THIS FEATURE TURNED ON,
  |HARDWARE IN THE TAPE CONTROL UNIT WRITES DATA AT A MUCH
  |HIGHER DENSITY THAN NORMAL, ALLOWING FOR MORE DATA ON A
  |VOLUME.
  
  |WARNING:  READING COMPACTED DATA FROM TAPE WILL CAUSE SOME
  |IMPACT ON PERFORMANCE UNDER DB2.
  
  |WARNING:  DATA THAT WAS WRITTEN TO TAPE USING DATA COMPACTION
  |CAN ONLY BE READ BACK USING A DEVICE THAT SUPPORTS THE IDRC
  |FEATURE. THIS COULD BE A CONCERN WHEN YOU SEND ARCHIVE TAPES
  |OFF SITE FOR REMOTE RECOVERY PURPOSES.
  
  NOTES:
  - AFTER APPLYING THE PTF YOU MUST USE ONE OF THE FOLLOWING
    PROCEDURES TO REASSEMBLE DSNZPARM:
    1) GO THROUGH THE INSTALL CLIST IN UPDATE MODE USING
       DSNTIDXA (AND NOT DSNTIDxx) AS INPUT MEMBER SINCE
       THIS FIX UPDATES DSNTIDXA TO REFLECT NEW DEFAULT VALUE
       FOR COMPACT DATA IN DSNTIPA.
    2) EDIT EXISTING DSNTIDxx MEMBER TO REFLECT COMPACT
       DATA = NO BEFORE RUNNING DSNTIJUZ.
  
       IN ADDITION TO THE FOLLOWING INFORMATION, SEE PL68190:
    FAILURE TO FOLLOW THESE PROCEDURES WILL RESULT IN
    COMPACT DATA = YES AS WELL AS OMISSION OF DEFAULT VALUE
    FOR COMPACT DATA IN NEWLY CREATED DSNTIDXX MEMBER.
    FAILURE TO REASSEMBLE DSNZPARM (JOB DSNTIJUZ) WILL
    RESULT IN DB2 RESTART FAILING WITH MSGDSNJ060I.
  
  - THE PERFORMANCE DEGRADATION WITH THE IDRC FEATURE WHEN READING
    BACKWARD ON COMPACTED DATA SHOULD BE ADDRESSED TO THE DFP
    TEAM. SEE INFORMATION APAR II04191 FOR MORE INFORMATION ABOUT
    THE IDRC FEATURE.  (DFP TAPE ERP 566528401 or 5695DF110)
  
  Additional keywords: 3490 D/T3490 3490E D/T3490E
     There are some models of the 3490 that always use the
  IDRC feature. On these models the data will be compacted
  regardless of the dsnzparm setting.  So, beware ARCHIVE read
  operations directed at these 3490E/IDRC devices can be very
  very time consuming.  DB2 will issue the READ BACKWARD command,
  the 3490E will fail the request, ERP will handle the error,
  the drive will then be repositioned  to READ the block
  forward.  This at mimimum, triples the I/O read time of the
  DB2 ARCHIVE read request.
  

Temporary fix

Comments

• DB2INFO: IEC707I
  

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UL76464 UL76465

Modules/Macros

•    DSNDARVP DSNDQWPZ DSNJDS01 DSNJS001 DSNTIDXA
  DSNTIJUZ DSNTINST DSNTIPA  DSNWVZPM DSN4XA1  DSN4XA2  DSN4XA3
  DSN4XA4  DSN4XA5  DSN4XA6  DSN6ARVP
  

Fix information

• Fixed component name

  5740 IBM DATABA

• Fixed component ID

  5740XYR00

Applicable component levels

• R210 PSY UL76464

     UP90/07/30 P F006

• R220 PSY UL76465

     UP90/07/27 P F006

Fix is available

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