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From: | Paolo Bonzini |
Subject: | Re: [Qemu-devel] check trim/unmap |
Date: | Tue, 28 Jan 2014 11:46:52 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 |
Il 28/01/2014 11:31, ching ha scritto:
My config is Gentoo x64 stable branch, kernel 3.10, libvirt 1.1.3, qemu 1.5, lvm2(non-thin) on ssd How can i check that if: 1. qemu receives trim/unmap from guest 2. qemu is punching hole/issue blkdiscards/writing zeros?
First of all, I suggest that you use current QEMU git. The trim/unmap feature was completed after 1.7 was released.
To use trim/discard, you need to use the discard=on option for QEMU's -drive command-line option. You also need to use cache=none (because of a Linux kernel bug, QEMU may disable thin provisioning in other cache modes).
In libvirt, this means adding cache='none and discard='on' like this: <driver name='qemu' type='qcow2' cache='none' discard='on'/>You can check if QEMU is punching a hole into a file using "qemu-img map" on the file. You must not run "qemu-img map" while the VM is running though; that can give incorrect results. There is no equivalent for block devices yet.
Paolo
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