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Re: [Qemu-devel] [RFC] Disk integrity in QEMU

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] [RFC] Disk integrity in QEMU
Date: Fri, 10 Oct 2008 09:54:14 +0200
User-agent: Thunderbird (X11/20080723)


> Read performance should be unaffected by using O_DSYNC.  O_DIRECT will
> significantly reduce read performance.  I think we should use O_DSYNC by
> default and I have sent out a patch that contains that.  We will follow
> up with benchmarks to demonstrate this.

So O_SYNC on/off is pretty much equivalent to disk write caching being
on/off, right?  So we could make that guest-controlled, i.e. toggeling
write caching in the guest (using hdparm) toggles O_SYNC in qemu?  This
together with disk-flush command support (mapping to fsync on the host)
should allow guests to go into barrier mode for better write performance
without loosing data integrity.


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