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Re: [Qemu-discuss] storage for qemu images

From: Fam Zheng
Subject: Re: [Qemu-discuss] storage for qemu images
Date: Thu, 28 Jul 2016 13:26:03 +0800
User-agent: Mutt/1.6.1 (2016-04-27)

On Wed, 07/27 15:32, Patrick Dumais wrote:
> Hi, I'm trying to figure out where is the best place to store qemu disk
> images.
> I am using qcow2 format on a raid1 built from 2 7200RPM hdd.
> I am considering moving the images on a ssd (not raid). The move to ssd
> would increase performances but the drawback is that I would not be on raid1
> anymore (and it is not an option for me right now to make a raid1 ssd)
> Knowing how the block cache works under linux, and the fact that I have
> 64gig of ram on my server, I'm wondering if the ssd would make a big
> difference anyway. All blocks read from the storage device will end up in
> the block cache making the backing device speed irrelevant to some degree.
> Am I right? So I'm tempted to keep the images on the raid device.

It depends.

If you use cache=none, you'd rely on guest page cache, because at host side
QEMU then uses O_DIRECT IO which bypasses host page cache.


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