Default use of caching on raw volumes

[Oliver Brakmann]

On 2010-09-01 21:19, Nikolai K. Bochev wrote:

> And if testing shows things are ok, would there be any merit in changing either libvirt or virt-manager to do this by default just for ubuntu ( not really sure what upstream will do about it ) ? 

FWIW, I would welcome such a change myself. Adding the cache='none'
directive to a VM's .xml file is the very first thing I do after its
installation, for performance reasons.

I have been running several VMs (all Lucid) for about four months now
that way, without ever encountering any issues¹.

The host is also Lucid, with unattended-upgrades set to automatically
reboot the machine when necessary, so the VMs sometimes just get killed.


Regards,
Oliver


1) well, besides that disk I/O from the guests is still too slow for my
taste.  I get near native speed (about 80 MB/s) using direct i/o during
tests with dd, but regular i/o during normal operation is only about 35
MB/s.  If anyone knows how to force direct i/o on all processes (or
something with similar results), please let me know.