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Q: How to extend VSAM file?
Answer:
ALTER ds.name ADDVOLUMES(vol). Or secondary allocation triggers extension. RECORDS/CYLINDERS secondary amount. Up to 255 extents per volume. May need to reorganize if fragmented.
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Q: Explain SPACE parameter options
Answer:
SPACE=(unit,(primary,secondary,directory)). Unit: TRK/CYL/block-size. Primary allocated first, secondary in 15 increments. Directory only for PDS. RLSE releases unused. CONTIG requires contiguous. Example: SPACE=(CYL,(10,5,20),RLSE)
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Q: What is REGION parameter?
Answer:
REGION specifies memory limit. REGION=0M means no limit (use system default). REGION=4M limits to 4MB. On JOB card affects all steps, on EXEC affects that step. Below 16M line: REGION=2048K. Modern systems often use REGION=0M.
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Q: How to check job status?
Answer:
SDSF DA/ST panels show jobs. TSO STATUS command. JES2 J'jobname'. JESMSGLG shows JCL, allocation. JESYSMSG has error details. Return code in JESMSGLG. Condition codes per step. Check SYSOUT for program output.
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Q: What is FREE parameter?
Answer:
FREE specifies when to release allocation. FREE=END (default) at step end. FREE=CLOSE when file closed. FREE=CLOSE allows reuse within step. Reduces concurrent allocations. Helps resource-constrained systems.
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Q: What is PERFORM parameter?
Answer:
PERFORM assigns service class. PERFORM=n (1-999). JES/WLM determines resource allocation. Higher may get more resources. Installation dependent. Modern systems use WLM service classes instead.
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Q: How to allocate SYSDA?
Answer:
UNIT=SYSDA for disk. Generic device group. Installation defines SYSDA contents. Usually includes all available disk. SMS may direct allocation. UNIT=3390 for specific device type. SYSDA preferred for portability.
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Q: What is RLSE subparameter?
Answer:
RLSE releases unused space at close. SPACE=(CYL,(10,5),RLSE). Returns unused secondary allocations. Good practice for new datasets. Saves disk space. May cause allocation issues if reextended.
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Q: Explain storage group
Answer:
Storage group defines volumes for data. CREATE STOGROUP name VOLUMES(vol1, vol2). Tablespaces assigned to stogroups. DB2 manages space within. PRIQTY/SECQTY control allocation. Foundation of storage management.
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Q: Explain UNIQUE vs SUBALLOCATION
Answer:
UNIQUE cluster gets own VSAM dataspace. SUBALLOCATION shares space with others. SUBALLOCATION deprecated, use UNIQUE. Modern systems prefer UNIQUE for isolation.
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Q: How to handle status 96?
Answer:
Status 96 is no DD statement for file. Check JCL has correct DD name. May be dynamic allocation failure. DD name must match SELECT ASSIGN. Case sensitive in some systems.
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Q: What is ORDERED attribute?
Answer:
ORDERED on DEFINE allocates volumes in specified order. Without ORDERED, system chooses. ORDERED ensures predictable allocation. May be important for performance tuning.
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Q: What is MSGLEVEL parameter?
Answer:
MSGLEVEL=(statements,messages). Statements: 0=JOB only, 1=all JCL, 2=input JCL. Messages: 0=completion only, 1=all including allocation. MSGLEVEL=(1,1) shows everything. MSGLEVEL=(0,0) minimal output. Affects JESMSGLG.
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Q: What is UNIT parameter?
Answer:
UNIT specifies device type. UNIT=SYSDA (direct access), UNIT=TAPE, UNIT=3390. UNIT=AFF=ddname shares device. UNIT=(SYSDA,2) allocates 2 volumes. SMS may override. UNIT=VIO for virtual I/O (memory only).
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Q: What is GETMAIN?
Answer:
GETMAIN allocates temporary storage. EXEC CICS GETMAIN SET(pointer) LENGTH(size) INITIMG(X'00'). Returns pointer. Use for dynamic memory. FREEMAIN releases. SHARED for multi-task access. Automatic cleanup on task end.
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Q: How to allocate PDSE?
Answer:
DSNTYPE=LIBRARY creates PDSE. Better than PDS: dynamic directory, member-level sharing, no compression needed. Or DATACLAS with PDSE attribute. Cannot convert back to PDS easily. Recommended for new PDSes.
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Q: How to use DYNAM in JCL?
Answer:
Dynamic allocation via BPXWDYN or TSO ALLOC. From program: call BPXWDYN with parm string. JCL can't do dynamic allocation itself. Programs allocate as needed. More flexible than static JCL allocation.