From: Christoph Hellwig <hch@lst.de>
To: Chunqiang Tang <ctang@us.ibm.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249%
Date: Wed, 19 Jan 2011 16:25:55 +0100 [thread overview]
Message-ID: <20110119152555.GA6763@lst.de> (raw)
In-Reply-To: <OF09F711B1.7B153722-ON8525781D.00532597-8525781D.0053E720@us.ibm.com>
On Wed, Jan 19, 2011 at 10:17:47AM -0500, Chunqiang Tang wrote:
> Thank both of you for the explanation, which is very helpful to me. With
> FVD's capability of eliminating the host file system and storing the image
> on a logical volume, then perhaps we can always use O_DSYNC, because there
> is little (or no?) LVM metadata that needs a flush on every write and
> hence O_DSYNC does not add overhead? I am not certain on this, and need
> help for confirmation. If this is true, the guest does not need to flush
> the cache.
O_DSYNC flushes the volatile write cache of the disk on every write,
which can be very ineffienct. In addition to that image formats really
should obey the configurable caching settings qemu has, they exist for
a reason and should be handled uniformly over different image formats
and protocol drivers.
next prev parent reply other threads:[~2011-01-19 15:27 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-04 21:44 [Qemu-devel] [RFC] Propose the Fast Virtual Disk (FVD) image format that outperforms QCOW2 by 249% Chunqiang Tang
2011-01-05 17:29 ` Anthony Liguori
2011-01-14 20:56 ` Chunqiang Tang
2011-01-19 1:12 ` Jamie Lokier
2011-01-19 8:10 ` Stefan Hajnoczi
2011-01-19 15:17 ` Chunqiang Tang
2011-01-19 15:25 ` Christoph Hellwig [this message]
2011-01-19 23:56 ` Jamie Lokier
2011-01-19 15:51 ` Christoph Hellwig
2011-01-19 16:21 ` Chunqiang Tang
2011-01-19 16:42 ` Christoph Hellwig
2011-01-19 17:08 ` Chunqiang Tang
2011-01-19 17:25 ` Christoph Hellwig
2011-01-06 9:17 ` Stefan Hajnoczi
2011-01-15 3:28 ` Chunqiang Tang
2011-01-15 17:27 ` Stefan Weil
2011-01-20 2:59 ` Chunqiang Tang
[not found] ` <AANLkTinw2S2dzKoeFK-dBP6b36J+VNLjb3f-vbkKm3Fz@mail.gmail.com>
2011-01-17 10:37 ` Stefan Hajnoczi
2011-01-18 20:35 ` Chunqiang Tang
2011-01-19 0:59 ` Jamie Lokier
2011-01-19 14:59 ` Chunqiang Tang
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