Right, on a normal load basis, this is correct. But, in most "normal load" machines, there are abnormal times. Such as applying a service pack, or a runaway program that eats up storage, or some bogus process (or dumb user) starting up VNCSERVER, over and over (multiple copies running), or.....
In a memory constrained system, it may be better (definitely for test/development systems) to have swap go to dasd. Then, you are only impacting that machine. When you have a big impact on the paging system, almost everyone (including production) can be impacted. Now, what is a major impact? If paging is on escon, 100 paging I/O per second was noticeable. Now I'm on 200 MB Ficon/2 channels, I've driven paging up to 1,000 I/O per sec and got no complaints. I don't know where that "knee" is, in my particule environment. But I'm pretty far away from it. The point being is, if you are near your "paging knee", swapping to real disk is better for the overall VM system, then a process that starts pounding vdisk and throwing your paging system out of whack. Actually, Mark, we agree on the basics of vdisk/swap. But I have never seen a paging system that couldn't be swamped. How many times have I PEEKed a file, should have been 10,000 lines, but it was 1,000,000 lines (or 10 million lines), and watch the paging system, deal with my error. <G> Like anything, vdisk can be abused. The question I would like to send out to all.... Has anyone else experienced the problem where vdisk abuse causes your VM paging system high enough activity to impact your other production machines? Or am I just lucky? Tom Duerbusch THD Consulting >>> [EMAIL PROTECTED] 2/23/2007 1:33 PM >>> >>> On Fri, Feb 23, 2007 at 1:48 PM, in message <[EMAIL PROTECTED]>, Tom Duerbusch <[EMAIL PROTECTED]> wrote: > To some extent, I agree with your VM systems programmer. IF you are in > a VM paging state, adding actively used vdisk, may not be the best thing > for you to do. The recommendation to use VDISK for swap is intended to be used in conjunction with a recommendation to shrink your virtual machines down as much as possible, thus reducing the degree to which you're over-committing real storage. If you exchange virtual/real storage for an increase in VDISK I/Os, you can usually manage to come out ahead of the game. The tolerable level of VDISK I/Os is surprisingly high (at least to me). Mark Post ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
