🚀 go-pugleaf

Nigel Arnot <NRA%ipg.ph.kcl.ac.uk@nsfnet-relay.ac.uk> writes:
> Some of you may have noticed my recent posting to info-vax about VMS failing
> to allocate a pagefile on a slightly fragmented disk, and what to do about
> it. For those who didn't, the problem was that SYSGEN CREATE was failing to
> allocate an 80000 block pagefile on a disk with around 200000 blocks free
> in fragments of size over 6000 blocks. What it was doing was building a
> file out of about four decent-sised fragments, and then filling the header
> with all sorts of mostly tiny fragments presumably out of the extent cache.

This is documented behaviour of the CBT (contiguous best try) allocation
option, which SYSGEN is using. It will look for suitable extents only
a limited number of times, then revert to the "standard" practice.

> I have now found another funny: the same problem in reverse. A user ran
> a FORTRAN program that generates two output files: the first stays small,
> the second ends up at around 3000 blocks, both are opened 'NEW' (ie empty)
> and filled with sequential writes.

Just recently I've seen the same with DECPs (VPA's new name) .CPD files,
which get pre-allocated at different (large) sizes every day; this *may*
have something to do with the availability of free extents, but I've no
real clue yet. This is on VMS 5.4-3.

Wolfgang J. Moeller, GWDG, D-3400 Goettingen, F.R.Germany | Disclaimer ...
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