ACP DATACHECK

ACP_DATACHECK
System parameter
Class ACP Attributes DYNAMIC

ACP_CHECK is a bitmask system parameter that controls the consistency of checks performed on internal file system metadata such as file headers.

Bit	Description
0	Set this bit to perform consistency checks on read operations. When this bit is set, the IO$M_DATACHECK function modifier is automatically set on all subsequent IO$_READLBLK operations that read file system metadata (see the HP OpenVMS I/O User's Reference Manual).
1	Set this bit to perform consistency checks on write operations. When this bit is set, the IO$M_DATACHECK function modifier is automatically set on all subsequent IO$_WRITELBLK operations that read file system metadata (see the HP OpenVMS I/O User's Reference Manual).
2	Set this bit to perform read-after-write consistency checks. This is similar to setting bit 1, except that in this case the file system does the checks, not the lower level device or disk driver. Note that read-after-write consistency checks are not allowed on deferred writes. Deferred writes are turned off if this bit is set.
3	Reserved for VSI use only; must be zero.
4	Reserved for VSI use only; must be zero.
5,6	see How to set bits 5 and 6 below
7	Reserved for VSI use only; must be zero.

How to set bits 5 and 6

To check that...	Select this level	Set bit 6 to	Set bit 5 to
The block is a valid directory block (reads only)	0	0	0
The block is a valid directory block (reads and writes)	1	0	1
The block is a valid directory block and contains valid entries (reads and writes)	2	1	0
The block is a valid directory block and contains valid entries in correct alphanumeric order (reads and writes)	3	1	1