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Storage Layout 
Cross Reference (Contains links to field and bit definitions)
Programming Interface Information:
This information is NOT intended to be
used as Programming Interfaces of z/VM.


  ALOCEXT Prolog Top of page
 
 NAME       : HCPALOC
 DESCRIPTION: DASD allocation record mapping for
              EXTENT-BASED ALLOCATION MAPPING.
 DSECT      : ALOCEXT
 FUNCTION   : Maps the DASD allocation record for system owned
              volumes with EXTENT-BASED ALLOCATION MAPPING.
 LOCATED BY : n/a
              exists only temporarily in storage,
              resides in block numbers 3 and 4 of
              an FBA DASD formatted for CP use
              For CKD and ECKD DASD, resides on
              cylinder 0, head 0, record 4.
 CREATED BY : ICKDSF
              when an FBA DASD is formatted for ESA
              CP use, or a CKD/ECKD DASD with
              more than ALOCMAXCM cylinders is
              formatted for CP use.
 DELETED BY : n/a
              exists in storage only until the in
              storage allocation map is built
 NOTES      :
  or FBA
              The FBA allocation record resides on FBA volumes formatted
              for CP use in the reserved pages, blocks 3 & 4.  There are
              two versions of the FBA allocation record, one for volumes
              formatted for 370 CP (which ESA CP can use), and one for
              volumes formatted for ESA CP.  The two versions map almost
              exactly the same.  The ESA version has an indicator that
              this is an extent-based allocation map as well as ESA
              allocation types.
              Volumes which are formatted for ESA CP use are marked by
              the presence of the string "CPVOL" in the volume owner
              area of the OS volume label record (block 1).
              FBA volumes which are formatted for 370 CP use are marked
              by the presence of the string "CP370" in the volume owner
              area of the OS volume label record (block 1).  FBA volumes
              formatted for 370 CP are usable by ESA CP without
              reformatting.
              The layout of the blocks in the reserved pages of FBA
              volumes is:
              0 - IPL record
              1 - OS VOL1 volume label record
              2 - VTOC - OS FORMAT 4 & FORMAT 5 labels
              3-4 - Allocation Record extent map
              5-12 - Initialized to 0
              13-31 - Reserved, initialized to 0.
  or FBA and CKD/ECKD
              Note that the length of the allocation record is variable
              depending on the number of extents.  The overall length of
              the allocation record is determined by multiplying the
              number of entries (found in bytes 3-4 of the first entry)
              by the length of an entry, and adding one (the next byte
              after the last entry is marked with X'FF').
              The allocation type values for all DASD formatted for ESA
              CP are the same for all types of DASD (CKD, ECKD, FBA).
 
 
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 ALOCEXT DSECT Top of page
Hex Dec Type/Val Lng Label (dup) Comments ---- ---- --------- ---- -------------- -------- 0000 0 Structure ALOCEXT DASD allocation record mapping for 0000 0 Bitstring 12 ALOCEENT (0) Extent map entry 0000 0 Bitstring 1 ALOCETYP Extent allocation type .... .... ALO370TE X'00' ALO370TE 370 FBA allocation type 'TEMP' .... ...1 ALO370PE X'01' ALO370PE 370 FBA allocation type 'PERM' .... ..1. ALO370TD X'02' ALO370TD 370 FBA allocation type 'TDSK' .... .1.. ALO370DR X'04' ALO370DR 370 FBA allocation type 'DRCT' 1... .1.. ALO370AD X'84' ALO370AD 370 FBA type in-use DRCT space .... 1... ALO370PA X'08' ALO370PA 370 FBA allocation type 'PAGE' ...1 .... ALO370DU X'10' ALO370DU 370 FBA allocation type 'DUMP' ...1 .1.. ALO370OV X'14' ALO370OV 370 FBA allocation type 'OVRD' ...1 11.. ALO370AO X'1C' ALO370AO 370 FBA type in-use OVRD space 0001 1 Bitstring 1 ALOCECNT Volume allocation contents - contains all of the extent map entry ALOCETYP bytes ORed together (valid only in first extent map entry on ESA formatted volumes, not valid for volumes formatted for 370) 0002 2 Signed 2 ALOCEECT Count of allocation extent map entries. Also, has indicator that this is an extent-based map. (Both count and indicator are valid only in 1st extent map entry.) 0004 4 Signed 4 ALOCESTR Extent start slot number FBA Extent start cyl number E/CKD 0008 8 Signed 4 ALOCEEND Extent end slot number FBA Extent end cyl number E/CKD 000C 12 Bitstring 1 ALOCENXT (0) Next extent entry 1111 1111 ALOCEND X'FF' ALOCEND Marks the end of the allocation map .1.1 .1.1 ALOCFMXX 85 ALOCFMXX Maximum number of extents allowed in one allocation map (FBA) .1.1 ..11 ALOCFOMX 83 ALOCFOMX Maximum number of extents allowed in one FBA alloc map when ownership information is written after the end of the map ALOCENXT ALOCEMXX 340 ALOCEMXX Maximum number of extents allowed in one allocation map (E/CKD) ALOCENXT ALOCMAXCM 4079 ALOCMAXCM Maximum number of cylinders for a cylinder based map. 0000000C ALOCEENL *-ALOCEENT Length of an extent entry 0002 2 Bitstring 1 ALOCEFLG Holds flag indicating this is the extent-based allocation map. Note that the other bits in this byte are NOT available to use as this field overlaps ALOCEECT. 1... .... ALOCEXTM X'80' ALOCEXTM Indicates this is the extent based allocation map. 0003 3 Bitstring 1 * Do not use Part of remap.
 
 
  ALOCEXT Storage Layout Top of page
 
          
*** ALOCEXT - DASD allocation record mapping for
*
*     +------+------+-------------+---------------------------+
*   0 |:CETYP|:CECNT|  ALOCEECT   |         ALOCESTR          |
*     +------+------+-------------+---------------------------+
*   8 |         ALOCEEND          |
*     +---------------------------+
*
*** ALOCEXT - DASD allocation record mapping for
          
*** Overlay for ALOCEECT in ALOCEXT
*
*                   +------+------+
*   0 ...         2 |:CEFLG|//////| 4
*                   +------+------+
*
*** Overlay for ALOCEECT in ALOCEXT
 
 
  ALOCEXT Cross Reference Top of page
 
 
Symbol         Dspl Value
-------------- ---- -----
ALOCECNT       0001
ALOCEECT       0002
ALOCEEND       0008
ALOCEENL       000C 0000000C
ALOCEENT       0000
ALOCEFLG       0002
ALOCEMXX       000C ALOCENXT
ALOCEND        000C FF
ALOCENXT       000C
ALOCESTR       0004
ALOCETYP       0000
ALOCEXTM       0002 80
ALOCFMXX       000C 55
ALOCFOMX       000C 53
ALOCMAXCM      000C ALOCENXT
ALO370AD       0000 84
ALO370AO       0000 1C
ALO370DR       0000 04
ALO370DU       0000 10
ALO370OV       0000 14
ALO370PA       0000 08
ALO370PE       0000 01
ALO370TD       0000 02
ALO370TE       0000 00
 
This information is based on z/VM 7.3.0 Last updated on 22 Jun 2022 at 15:57:41 EDT.
Copyright IBM Corporation, 1990, 2022