On Thu, Apr 30, 2009 at 6:21 PM, Rich Smrcina <rsmrc...@wi.rr.com> wrote:
> Both ESALPS and the Performance Toolkit will show that an unused Vdisk will > use very little storage. Even if you do manage to start using it, after a > certain amount of time it is likely to get paged out if unreferenced long > enough. Barton has been presenting these topics at SHARE and WAVV for > several years now, they should be well burned in... I can't speak for the other product, but you could be right ;-) The reason we tell you not to fill that second overflow VDISK is not because it would take up too much real memory, but because it will make things very slow even though you did not want it to. And because when VDISK gets paged out, you need twice the amount in page space. The overflow swap VDISK is like what normal swap is for Linux on other platforms: it's supposed not to get used unless the application went out of its mind or something like that. Assuming that not all servers go crazy at the same time, you can probably stand it reasonably well if you set up monitoring. When the workload slightly grew beyond expectation, it will drip into the 2nd VDISK only a little. That means it will take a while before it really takes up space, and you have time to handle it. Even when multiple servers seem to outgrow plan. As long as it is VDISK, people will not notice and you can plan for change. But when your 2nd VDISK is real disk, performance will be bad (even with only a little swapping) and big badges will prevent easy planning of the change. Rob -- Rob van der Heij Velocity Software http://www.velocitysoftware.com/
