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Q: What is RECORDING MODE for files?
Answer:
RECORDING MODE specifies record format: F=fixed, V=variable, U=undefined, S=spanned. RECORDING MODE IS V for variable records. Affects how records are blocked and how length is tracked. Must match JCL DCB specifications.
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Q: What is file status 39?
Answer:
Status 39 is file attribute mismatch. JCL attributes don't match cluster. Check: RECFM, LRECL in JCL vs cluster. May need to omit DCB parameters. VSAM doesn't use standard DCB.
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Q: Explain DCB parameter
Answer:
DCB defines Data Control Block: RECFM (F/FB/V/VB/U), LRECL (record length), BLKSIZE (block size). DCB=(RECFM=FB,LRECL=80,BLKSIZE=27920). Can inherit from existing dataset. LRECL required for new datasets. BLKSIZE=0 lets system optimize.
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Q: How to concatenate datasets?
Answer:
Stack DD statements: //INPUT DD DSN=FILE1,DISP=SHR // DD DSN=FILE2,DISP=SHR. No DD name on continuation. Read consecutively as one file. Different LRECL needs LRECL on first DD or DCB parameter. Concatenation limit varies by system.
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Q: Explain RECFM options
Answer:
RECFM defines record format. F=fixed, V=variable, U=undefined. B=blocked, A=ASA control, M=machine control, S=spanned. Combinations: FB=fixed blocked, VBS=variable blocked spanned. Match program expectations.
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Q: Explain BUFNO parameter
Answer:
BUFNO sets number of I/O buffers. DCB=(BUFNO=5). More buffers improve sequential performance but use memory. System default often 5. VSAM uses different buffering (BUFNI, BUFND). Too many can waste memory.
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Q: What is FILEDATA parameter?
Answer:
FILEDATA specifies DCB for NFS/USS. FILEDATA=TEXT or BINARY. TEXT handles line endings. BINARY transfers unchanged. On PATH DD statements. Affects how data converted between systems.
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Q: What is LRECL=X?
Answer:
LRECL=X means system-determined length. Usually for RECFM=U or special files. System calculates based on BLKSIZE or file characteristics. Not common for normal datasets. Used with certain utilities.
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Q: What is DATACLAS parameter?
Answer:
DATACLAS assigns SMS data class. DATACLAS=classname. Defines DCB attributes, space, data type. ACS routines may assign automatically. Overrides explicit DCB. Simplifies JCL. Installation-defined classes.
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Q: Explain REFDD parameter?
Answer:
REFDD references DD for attributes. DCB=*.STEP.DD or REFDD=ddname. Copies DCB info. Similar to VOL=REF. Useful for consistent attributes. Referenced DD must be allocated first.
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Q: Explain EROPT parameter?
Answer:
EROPT specifies error handling. DCB=(EROPT=ABE/ACC/SKP). ABE=abend on error, ACC=accept and continue, SKP=skip block. For tape I/O errors. Program may handle differently. Default is ABE.
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Q: Explain SMS-managed storage
Answer:
SMS (Storage Management Subsystem) manages dataset placement. Specify STORCLAS, MGMTCLAS, DATACLAS in DD. DATACLAS sets DCB attributes, STORCLAS controls placement, MGMTCLAS defines retention. SMS uses ACS routines for assignment.
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Q: How to define PDS?
Answer:
//PDSOUT DD DSN=MY.PDS,DISP=(NEW,CATLG),SPACE=(CYL,(5,1,10)),DCB=(RECFM=FB,LRECL=80). Directory blocks (10) required for PDS. Or DSNTYPE=LIBRARY for PDSE. PDSE allows dynamic directory expansion, member-level sharing.
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Q: Explain LIKE parameter
Answer:
LIKE copies DCB attributes from existing dataset. DCB=*.STEP1.DD or LIKE=catalog.dataset. Simplifies JCL. Model dataset must exist or be allocated earlier. Override specific attributes: DCB=(LIKE=...,LRECL=100).
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Q: What is KEYLEN parameter?
Answer:
KEYLEN specifies key length for new dataset. DCB parameter for VSAM-like. Or VSAM DEFINE CLUSTER KEYS(length offset). Length 1-255. Required for indexed organization. Offset from 0 or 1 depending on context.