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

Avi Kivity
2009-01-04T19:50:20Z

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.

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