Disable Harddisk Caching for qcow2

[nmue]

Hi,

We are evaluating KVM/proxmox to replace our current virtual environment. I made some tests on CPU and Harddisk. CPU is faster in KVM (about 10%) but the Harddisk is about 50% slower than our current system.

I started googling and reading trough this forums and couldn't find any hints. In the KVM manpage there is some info about the caching part of the harddisk. They say if you want more performance with your qcow2 image, the cache should be disabled (even tough this can lead to problems if the host loses power or something like that).

Well actually I would like to redo the tests with caching disabled, but how do I do it in proxmox? Didn't found any option on this.

 

[tom]

Hi,

We are evaluating KVM/proxmox to replace our current virtual environment. I made some tests on CPU and Harddisk. CPU is faster in KVM (about 10%) but the Harddisk is about 50% slower than our current system.

I started googling and reading trough this forums and couldn't find any hints. In the KVM manpage there is some info about the caching part of the harddisk. They say if you want more performance with your qcow2 image, the cache should be disabled (even tough this can lead to problems if the host loses power or something like that).

Well actually I would like to redo the tests with caching disabled, but how do I do it in proxmox? Didn't found any option on this.

you have several option to use storage:
see http://pve.proxmox.com/wiki/Storage_Model

so the questions is what you use and even more - how do you benchmark?

 

[ParanoiK]

That depends on configuration. You can easily disable cache by expanding one line in the config, for exaple you have file /etc/qemu-server/101.conf (or any other config):

scsi0: local:101/vm-101-disk-1.raw

You can change this to:

scsi0: local:101/vm-101-disk-1.raw,cache=none

More options about cache are in qemu documentation:
http://www.nongnu.org/qemu/qemu-doc.html#SEC10