Error when trying to move a virtual server between physical servers

Submitted by franksl on Tue, 09/28/2010 - 07:54

I have 4 identical server which are being controlled by cloudmin, all clustered to be able to use a backend clustered gfs2 storage. The virtual config files are stored in /xen, which is a lvm available on all of those 4 servers. New virtuals are created with lvm's, again available on all 4 servers on the shared storage.

I have created a virtual (test) server from a centos base image. As a test i try moving that virtual server from server 1 to server 2, which gives me the following "error" (?) .. " Moving Xen system from server1.adomain.com to server2.adomain.com ..

The host system server2.adomain.com is not suitable : Only 534 MB RAM would be free after creating this system, but the minimum is 1024 MB "

The virtual is created with 512Mb ram, on a 2G lvm partition.

The physical servers all have 32Gigs of ram, and at this point are empty (but for the one virtual on "server1".

Did i make at a certain point some configuration error or ... ? I haven't been able to figure out why it's refusing to move that virtual.

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Comments

Submitted by JamieCameron on Tue, 09/28/2010 - 11:46

That error means that Cloudmin thinks the target host system doesn't have enough free RAM. You can set a limit on the amount Cloudmin will ensure remains free at Host Systems -> Xen Host Systems -> target host -> Virtual system resource limits -> Memory to leave free.

You might want to lower that, perhaps all the way to 0 if your Xen host has a fixed amount of RAM reserved for it in the grub menu.lst file.

Submitted by franksl on Fri, 10/01/2010 - 09:37

Thanks for your reply.

Yes i know the setting, and changed that to 0 again, although I had only set that to 1Gb to leave free. However that doesn't change a thing. When trying to move the virtual, in the drop-down box where i can set the new host server, all servers there do not show the actual amount of free memory (like seen in eg "free -m" on physical server). At this point I've added like 6 servers available for XEN hosting, all have the same 'problem'. So somehow Cloudmin doesn't seem recognize the amount of free memory available for virtuals. It does see the total amount of mem (when seen through webmin on the local system) and the real amount of free memory there. So i'm puzzled still, I cannot find some setting where I have to set the amount cloudmin can use for virtualisation, besides the setting you are referring to.

Submitted by JamieCameron on Fri, 10/01/2010 - 12:28

The free memory shown by the free command can be quite different to that available for Xen, if you have memory reserved for the dom0.

If you select a host system from the left menu and click on Edit System, what does it show in the "Real memory used" and "Real memory for hosting" graphs?

Submitted by franksl on Fri, 10/08/2010 - 07:04

There it says:
Real memory used: 1.03 GB out of 30.97 GB
Real memory for hosting: 30.97 GB out of 31.99 GB

which I interpret as having ~31G free for hosting. Which is true actually.

Submitted by franksl on Fri, 10/08/2010 - 07:35

And after i posted my previous reply i tried another move of a running xen instance, and all of a sudden it worked, without me having changed any of the settings concerning memory. Weird. I was logged ssh into that xen virtual, had a ping running to "some outside server" and it barely dropped a ping. Which is a good thing :)

I'll keep doing some tests with this (manual and through auto-failover) and keep things posted here if they go wrong.

Submitted by JamieCameron on Fri, 10/08/2010 - 16:12

Ok, that's cool .. please let us know if this fails again, and if so how much memory is shown free for hosting on the target system (as that's the metric which Cloudmin uses to evaluate a transfer).