I am user Brazilian of z/VM and I had an incredible reduction of + 88% of paging for 0% with the update of z/VM of the V5R10 for the V5R20.
I recommend this procedure.
Thanks to all,
Fernando
2006/9/12, Rob van der Heij <[EMAIL PROTECTED]>:
On 9/12/06, Austin, Alyce (CIV) <[EMAIL PROTECTED]> wrote:
> In regards to paging, should MDC be off for a Linux guest
> running under z/VM? That is, MINIOPT NODMC to reduce paging?
There's no universal wisdom on that. Most of us agree that it is not
useful to use MDC on Linux swap disks. But swapping is done better to
VDISK anyway, so that is not really an issue. When there is no I/O to
the swap disk, NOMDC or not is a moot point as well (and you would not
bother selecting the disks for MOMDC). If you need to prevent MDC
using too much of your real memory, you must tune the arbiter.
Whether MDC is good for other Linux disks is the question. Ideally you
would rather have Linux to cache its data than have z/VM do MDC
(especially since MDC is not as effective). And Linux does that anyway
if you give it the memory. But Linux will continue to cache its data
even when it has little work to do and thus prevent the other Linux
servers (that may have work to do) from keeping their cache. If you'd
push hard enough, the Linux cache will be paged by z/VM and the result
of that is normally unpleasant.
The idea is that you keep the Linux servers relatively small. That way
they're not too much trouble for z/VM and suffer less from z/VM
paging. Obviously the small Linux servers have less room to cache
stuff and will be doing more I/O when they have work to do. The small
Linux servers now leave more room for z/VM MDC and it's the Linux
servers with I/O (the ones that have work to do) that take advantage
of that. This way you share the white space among the virtual servers.
There is a cost involved with sharing, like with any sharing. Whether
this works for you depends among others on the utilization of your
servers (percentage of time they have work to do).
Rob
--
Rob van der Heij
Velocity Software, Inc
http://velocitysoftware.com/
