[PVE-User] Very slow server (RAW IDE discs and KVM)

CoolCold coolthecold at gmail.com
Fri Aug 5 13:36:17 CEST 2011

I'm not expert in Proxmox (never used or even installed) but regarding
KVM - may be you should check "cache" policy for that machine(s) ? One
day I was installing Win7 inside KVM container and changing cache mode
helped me (i may be wrong but i set it to "none").

Quoting Tuning KVM[1]

QEMU also supports a wide variety of caching modes. Writeback is
useful for testing but does not offer storage guarantees. Writethrough
(the default) is safer, and relies on the host cache. If you're using
raw volumes or partitions, it is best to avoid the cache completely,
which reduces data copies and bus traffic:

 qemu -drive file=/dev/mapper/ImagesVolumeGroup-Guest1,cache=none,if=virtio

Hope this will help you.

[1] http://www.linux-kvm.org/page/Tuning_KVM

On Fri, Aug 5, 2011 at 3:10 PM, Erik van Ast <Erik.van.Ast at suzohapp.nl> wrote:
> Hi all,
> We have a PROXMOX 1.8 server running on a “4 x Intel(R) Core(TM)2 Quad CPU
> Q9650 @ 3.00GHz” CPU with 8GB RAM installed. At the moment 3 virtual servers
> are running on it (OpenSuse 11.2, Windows 2003 and Windows 2008) and one of
> my servers (Windows 2003, 2GB of RAM, 2 RAW IDE discs) is being extremely
> slow when writing data to it. We want to use this machine as file server, so
> we want to copy 180GB of data to it. The copying of data is almost finished
> now, but it took about 4 days to complete and we are on a 1Gbit connection
> internally so that shouldn’t make a difference. I saw that the machine is
> especially slow when copying large data over (like PST files), the speed
> than drops to 10-20Kbps instead of the multiple Mbps it should do.
> At the moment 6.37 of the 8GB have been takes by the machines so RAM
> shouldn’t be a problem and total CPU is 50% now, so that should also be no
> problem.
> When running task manager on the virtual server itself, nothing special is
> seen. No high CPU, no high RAM but the server is almost unresponsive. As
> soon as the server is finished copying, everything is back to normal speed
> Has anyone ever seen this and does anyone know how to solve it?
> Kind regards,
> Erik
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> pve-user mailing list
> pve-user at pve.proxmox.com
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Best regards,

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