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Fragmentation of INDEXF.SYS file?

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The Question is:

What is a good value of the 'Map area words in use' from a DUMP/HEADER command
 for an INDEXF.SYS file to watch for to trigger an offline defrag process?  Is
 there a maximum value?

The Answer is :

    The maximum size of the map area is 150 words. Each mapping pointer
    takes up 2 or 3 words. The Wizard therefore recommends anything over
    140 words to be the "red zone" for INDEXF.SYS, indicating that an
    offline defrag should be performed (either using BACKUP/IMAGE and restore,
    or using the DEFRAGMENT OFFLINE_VOLUME command in the Disk File Optimizer
    Note that wizard recommends *against* preallocating header space to
    INDEXF.SYS as it is very difficult to recover overallocations. If you
    have a disk with a full INDEXF.SYS, you will probably only need *ONE*
    BACKUP/IMAGE and restore over the life of the disk to enable INDEXF.SYS
    to expand to a size where it is possible to fill the disk. The Wizard
    has never come across a disk which has filled INDEXF.SYS twice.
    The reason for this problem in the first place was the algorithm for
    extending INDEXF.SYS. In OpenVMS V5.5-2 and below, it was exceedingly
    simple - a constant 1000 blocks. Moreover, there was no particular effort
    to allocate a contiguous extent. This algorithm was fine for disk sizes
    common at the time it was implemented, but has proven inadequate for
    modern, high capacity disks (say over 1GB).
    In OpenVMS V6 and higher, the extension algorithm takes into account the
    average file size on the disk and the amount of free space. It calculates
    the estimated size of INDEXF.SYS required to fill the disk and extends
    to that size. Furthermore, the extension is contiguous-best-try. The
    wizard is yet to see a single cases of INDEXF.SYS filling up on disks
    initialized on OpenVMS V6 or higher.

answer written or last revised on ( 4-JUN-2000 )

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