From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Poor Write I/O Performance on KVM-79 Date: Sun, 04 Jan 2009 21:48:15 +0200 Message-ID: <4961127F.7020700@redhat.com> References: <66c93b820901032203yc735b1g48d5bf19deffbfc@mail.gmail.com> <4960B88A.2010608@redhat.com> <33d560f70901041007u5d0231dp55b1ef525f2d3925@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Alexander Atticus , kvm@vger.kernel.org, Mark McLoughlin To: Rodrigo Campos Return-path: Received: from mx2.redhat.com ([66.187.237.31]:52926 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756950AbZADTuU (ORCPT ); Sun, 4 Jan 2009 14:50:20 -0500 In-Reply-To: <33d560f70901041007u5d0231dp55b1ef525f2d3925@mail.gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: 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. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.