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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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