|
From: | Pavel Butsykin |
Subject: | Re: [Qemu-block] [Qemu-devel] [PATCH v2 0/2] Truncate the tail of the image file in qcow2 shrinking |
Date: | Fri, 22 Sep 2017 15:33:18 +0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
On 22.09.2017 12:50, Daniel P. Berrange wrote:
On Fri, Sep 22, 2017 at 12:39:24PM +0300, Pavel Butsykin wrote:Now after shrinking the qcow2 image, at the end of the image file, there might be a tail that probably will never be used. Although it will not bring any tangible benefit, we can cut the tail if it is. Yes, it will not free up disk space, but if the blocks were be allocated sequentially and the image is not heavily fragmented then the virtual size of the image file will be commensurate with the real size. It also doesn't look like a great plus.. Well, at least we can discuss it.If the block backend has discard support enabled, can't we get the tail to be discarded rather than merely truncated ?
It has already been implemented. (see https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg04581.html)
Sorry, I just forgot to mention that this patch rebased on Max's block branch (https://github.com/XanClic/qemu/commits/block). Actually the truncation will always be done on the already discarded area. It can be useful only if the block backend doesn't support discard or a file system doesn't support sparse files.
Regards, Daniel
[Prev in Thread] | Current Thread | [Next in Thread] |