HP OpenVMS Systems

Ask the Wizard Questions

Tuning: Extent cache

The Question is:

When I do a SHOW DEVICE/FULL DIA9, the listing shows information
about the number of blocks in the extent cache. Where do I
find more information about WHAT the extent cache is?

The Answer is:

    $ mcr sysgen help param acp_extcache

      ACP_EXTCACHE

        ACP_EXTCACHE sets the number of entries in the extent cache.
        Each entry points to one contiguous area of free space on disk.
        A specification of 0 means no cache. Too small a value causes
        excessive XQP I/O operations, while too large a value causes
        excessive physical memory to be consumed by the extent cache.

    Also see Kirby McCoy's File System Internals book.