I look at a LOT of real data from a lot of real systems. So far, I've
not seen an installation where vdisk (correctly defined) impacts other
servers. If anybody has some, please send it (monitor data), I would
like to understand how that happens. Though I have heard of SAP servers
that do some rather strange things at startup.
Swap to virtual disk is better than 3 orders of magnitude faster than
dasd, i call dasd slow, but guess it's relative.
I have seen an installation that correctly defined the two vdisks, one
small, one large, set the alert, but reversed the priority so the big
disk was used and the little one was not. That would NOT be the
correctly defined vdisks.
Doug Shupe wrote:
Scott you hit this one on the head!
Penguins multiply rapidly, real memory tends to stay constant ($$$).
Sure VM is Great at paging but, like you say, impacting all the
Penguins? YMMV. Alerts are a must either way. When memory is at a
premium, one v-disk and the rest real disk is the way to go. DASD is not
'that' slow anymore.
Doug
----- Original Message -----
*From:* Scott Rohling <mailto:[email protected]>
*To:* [email protected] <mailto:[email protected]>
*Sent:* Wednesday, April 29, 2009 18:13
*Subject:* Re: SWAPGEN
Maybe -- but having a real disk (and setting an alert for that)
helps isolate the issue to a single guest rather than affecting
critical shared resources (in this case memory/paging) when a guest
starts swapping more than normal or than it 'should'.
I like the idea of having a 'failover' swap area on real disk --
whether you have a single VDISK or 2 prioritized ahead of it. I
guess whether it's waste of resource depends on your POV.. But your
point is taken..
Scott
On Wed, Apr 29, 2009 at 4:42 PM, Barton Robinson
<[email protected]
<mailto:[email protected]>> wrote:
giving real disks to swap is a real waste of resource. It is
much better to take the "extra disk resource" that you allocate
but never want to use, and assign it to z/VM paging to enhance
your paging subsystem. Then define two vdisks for swap,
prioritize them, and set an alert when the 2nd disk is being used.
Martin, Terry R. (LOCKHEED MARTIN Performance Engineering/CTR)
(CTR) wrote:
Hi
I am using SWAPGEN to define by z/Linux VDISKS I also want
to define a real disk for swap. My question is can I use
SWAPGEN to define a swap on real DASD? If you have an
example of the control card syntax to accomplish this that
would be great?
//Thank You,//
//Terry Martin//
//Lockheed Martin - Information Technology//
//z/OS & z/VM Systems - Performance and Tuning//
//Cell - 443 632-4191//
//Work - 410 786-0386//
//[email protected] <mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>//
