IIRC, pages read from SPOOL-resident DCSSs are counted as paging I/O, so the scenario you describe in your third paragraph is certainly a possibility.
Marty > -----Original Message----- > From: The IBM z/VM Operating System > [mailto:[EMAIL PROTECTED] On Behalf Of Bill Holder > Sent: Monday, May 19, 2008 3:30 PM > To: IBMVM@LISTSERV.UARK.EDU > Subject: Re: Mystery paging > > The dataspace usage is certainly a good thing to check, but there are at > least a couple of other possibilities: > > The paging rate numbers are across time, whereas the Q ALLOC PAGE output is > instantaneous. It could be that there's a low volume of paging to/from paging > DASD going on, but the pages that are read in are immediately changed, which > would cause CP to discard the copy out on paging DASD when CP notices the page > change. So it needn't be the same page read 13 times a second, it could be a > bunch of different pages which are then immediately changed, for which CP > then discards the paging DASD copy. > > I'd have to check, but it seems possible that demand paging of spool pages > from (and even possibly to) spool volumes could account for this, I'd have to > check how those get counted. In particular, if you have a very lightly used > NSS or DCSS, that only tends to be loaded by one user at a time, and it is > frequently purged and then reloaded, the initial page fault block reads from > spool might show up like this. > > - Bill Holder > z/VM development, IBM >