Re: Poor Write I/O Performance on KVM-79

Rodrigo Campos
2009-01-04T20:12:59Z

On Sun, Jan 4, 2009 at 5:48 PM, Avi Kivity <avi@redhat.com> wrote:
> Rodrigo Campos wrote:
>>>
>>> qcow2 will surely lead to miserable performance. raw files are better.
>>> best is to use lvm.
>>>
>>>
>>
>> What do you mean with best is to use lvm ?
>> You just say to use raw images on an lvm partition because you can
>> easily resize it ? Or somehow images only use the used space of the
>> raw file when used with lvm ? Or there's some trick to make it ?
>>
>
> Using lvm directly (-drive file=/dev/vg/volume) is both most efficient and
> most reliable, as there are only a small amount of layers involved.
> However, you need to commit space in advance (you can grow your volume, but
> that takes guest involvement and cannot be done online at the moment).
>
> Using a raw file over a filesystem will be slow since the host filesystem
> will be exercised, and due to fragmentation. Raw files only occupy storage
> as they are used, but they are difficult to manage compared to qcow2 files.
>
> Qcow2 files are most flexible, but the least performing.

Ahhh. Thanks a lot for the explanation :)

Rodrigo