Just a few general comments:
Paging space becoming full and paging errors are two different problems t
hat
manifest differently (though the latter can certainly contribute to the
former). Inadequate paging space will not lead to paging errors being
reported.
If paging space becomes full, paging will overflow to spool space, and
messages 401 (90% full) and 400 (100% full) will have been issued for pag
ing
space. If spool space also becomes full, those messages will also be iss
ued
for spool space, and a PGT004 hard abend will likely result.
If paging errors occur, there should be EREP messages. Message 0415 ("Si
x
continuous paging errors...") will only be issued if 6 paging IO requests
in
a row to a single volume all result in failures. This is really not like
ly
to be a hardware problem with modern highly cached virtual storage DASD
systems like Shark and such. These errors almost always occur on write
requests, as one slot is found to be "bad" (unusable), and the algorithm
bumps to the next available slot and tries it in turn. As others have
mentioned, it's almost always because a contiguous region of paging space
was either never formatted completely, or have since been overlaid by
something else (such as a minidisk). If a large enough area of paging sp
ace
is not correctly formatted, this can result in a PGT004 or FRF002 (or les
s
likely, SXP004) hard abend outage as CP finds no usable paging space to
write to, and storage starts filling up with queued 0415 and EREP message
s.
In my experience, such paging errors are overwhelmingly caused by lack of
(or improper) formatting, with minidisk overlays being a distant second,
and
actual disk hardware problems a very far distant third.
- Bill Holder, z/VM Development, IBM Endicott
