Path: utzoo!attcan!uunet!aplcen!samsung!emory!mephisto!ncar!ico!ism780c!randvax!ucla-an!stb!lampi
From: lampi@stb.uucp (Michael Lampi)
Newsgroups: comp.sys.apollo
Subject: Mixed SR10.2/SR9.7 filesystem performance
Summary: Number of Mounted Logical Volumes makes a difference
Message-ID: <1990Feb19.201057.10358@stb.uucp>
Date: 19 Feb 90 20:10:57 GMT
Reply-To: lampi@stb.uucp (Michael Lampi)
Organization: MDL Corporation, Torrance, CA
Lines: 23

The Apollo filesystem under SR9.7 (and probably still under SR10.2) experiences
a marked reduction in performance as one mounts additional logical disk
volumes on a particular node. The reason for this behavior was explained to
me as having to do with the fact that the relationship of UID's to volumes
is nearly nonexistant, and the OS has to do a lot of searching to find a
file amongst each volume. However, once the object (file) has been opened,
access to that file is very fast.

For example, if you have a floppy disk mounted along with a local winchester,
the OS will take a look at the floppy when you are trying to locate a file.
Of course, if the filesystem information of the floppy happens to be in RAM,
then this access will be much faster than if it has to be re-read from the
diskette.  This is why you will hear/see the floppy being accessed from time
to time when you haven't done anything to it for a long time. (Yes, I know
that paging also occurs if you've just written something to the floppy, but
this is after you've just mounted it and done nothing else.)

I suggest that you consider striping and cylinder stacking your DN-4000
disks together, making them 1 or two logical volumes. With your dual
controllers and 10.2 OS, you should get pretty good performance.

Michael Lampi            (213) 782-7888    Fax (213) 782-7927
MDL Corporation           PO Box 745, Torrance, CA  90508