2012/10/18 Mathok <math...@googlemail.com>
> > > 2012/10/17 Alan Johnson <a...@datdec.com> > >> On Wed, Oct 17, 2012 at 5:02 PM, Mathok <math...@googlemail.com> wrote: >> >>> Same here with ovirt 3.1.0-2 i can't see a change in the UI. But i'm >>> able to start more VMs and hava a higher usag of my swap partiotion so i >>> think the change had the desired effect >>> >> >> Oh, does this take advantage of host swap space as well? I thought I had >> read oVirt could do that somewhere, but I have been reading about so many >> different virtualization systems over the last few months that when the RHEV >> 3.1 Admin >> Guide<https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Virtualization/3.1-Beta/html-single/Administration_Guide/index.html>did >> not mention swap space in section "4.2.2.2. Memory Optimization >> Settings Explained", I was not sure if it applied here. This is all it >> says at the moment: >> >> "Memory page sharing allows virtual machines to use up to 200% of their >> allocated memory by utilizing unused memory in other virtual machines. This >> process is based on the assumption that the virtual machines in your Red >> Hat Enterprise Virtualization environment will not all be running at full >> capacity at the same time, allowing unused memory to be temporarily >> allocated to a particular virtual machine." >> >> >> Do you have a reference handy that confirms and explains this? I put >> some speedy SSDs in my hosts to hopefully take advantage of this (and maybe >> run gluster), so I am hoping to see that in print somewhere. I'll dig it >> up if you don't have it handy, but a confirmation that this is >> your experience and understanding would make me feel better in the mean >> time. >> > > let me explain my (now fixed) problem i have a ovirt host with 8 GB Ram > and 12 VMs every with 256 MB Physical Memory Guarantee. When i start my two > mysql-cluster vms they will use the 256 PMG plus 3,75 GB MS they have > defined a max of 4 GB MS. At this poitn now the problem begins the mysql > taken the hole memory in both vms and now there is no more free ram at the > host and it is not possible to start more vms. > > (this is also speculation im not a expert) So i need for my understanding > a higher rate of memory overcommit to be able to start all vms, and for > that the host must use the swap to have enough memory for overcomit to > start all vms and yes the higher the rate, the worse the performance. I'm > not sure if this is the right or good way tho fix this problem > > (sorry for my bad english I hope this is understandable) > > sorry i have no reference handy that confirm or explain this for ovirt. i have only combined my linux and vmware knowledge and i think that it will work in ovirt a almost equal way like vmware http://www.yellow-bricks.com/2011/08/18/swap-to-host-cache-aka-swap-to-ssd/where you can speed up the swap in a overcomit situation wit a ssd. On linux we can simply put the swap on a ssd and we have a very fast swap.
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