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Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format
From: |
Chunqiang Tang |
Subject: |
Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249% |
Date: |
Wed, 19 Jan 2011 11:21:07 -0500 |
> It's something filesystems have to deal with. Real storage is getting
> increasingly virtualized. While this didn't matter for the real high
> end storage which has been doing this for a long time it's getting more
> and more exposed to the filesystem. That includes LVM layouts and
> thinly provisioned disk arrays, which are getting increasingly popular.
> That doesn't matter the 64k (or until recently 4k) cluster size in qcow2
> is a good idea, we'd want at least a magnitude or two larger extents
> to perform well, but it means filesystems really do have to cope with
> it.
Yes, a fundamental and optimal solution would be changing guest file
systems, but it would take a much much longer route to introduce
virtualization awareness into all guest file systems and its also requires
changing the interface between the guest and the host.
> I/O into fully preallocated files uses exactly the same codepath as
> doing I/O to the block device, except for a identify logical to physical
> block mapping in the block device and a non-trivial one in the
> filesysgem. Note that the block mapping is cached and does not affect
> the performance. I've published the numbers for qemu in the various
> caching modes and all major filesystems a while ago, so I'm not making
> this up.
Preallocation is not a universal solution here, because it just defeats
the other goal: thin provisioning. Moreover, if preallocation is used, it
works best for RAW images and makes it unnecessary to use a compact image,
which is exactly one goal of FVD, i.e., allowing optionally disabling a
compact image data layout without giving up other features, e.g.,
copy-on-write.
- [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Chunqiang Tang, 2011/01/04
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Anthony Liguori, 2011/01/05
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Chunqiang Tang, 2011/01/14
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Jamie Lokier, 2011/01/18
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Stefan Hajnoczi, 2011/01/19
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Chunqiang Tang, 2011/01/19
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Christoph Hellwig, 2011/01/19
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Jamie Lokier, 2011/01/19
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Christoph Hellwig, 2011/01/19
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%,
Chunqiang Tang <=
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Christoph Hellwig, 2011/01/19
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Chunqiang Tang, 2011/01/19
- Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Christoph Hellwig, 2011/01/19
Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%, Stefan Hajnoczi, 2011/01/06