Re: [Xen-devel] [PATCH resend] libxl, hotplug/Linux: default to phy backend for raw format file, take 2

[Fabio Fantoni <fabio.fantoni@xxxxxxx>]

Il 12/01/2015 11:06, Ian Campbell ha scritto:
> On Mon, 2015-01-12 at 10:39 +0100, Fabio Fantoni wrote:
> > Il 12/01/2015 10:31, Ian Campbell ha scritto:
> > > On Mon, 2015-01-12 at 10:15 +0100, Fabio Fantoni wrote:
> > > > In the meantime, I saw this:
> > > > http://lists.xen.org/archives/html/xen-users/2015-01/msg00047.html
> > > > Based on the post above seems that phy will have important risk of data
> > > > loss if I understand good, from Ian Campbell post:
> > > > > xl also uses qdisk for raw disk images instead of loop+blkback which
> > > > > xend used, because there are concerns that the loop driver can lead to
> > > > > data loss (by not implementing direct i/o the underlying device, and/or
> > > > > not handling flushes correct, my memory is a bit fuzzy).
> > > Stefano already corrected me on this in this very thread.
> > >
> > > Ian.
> > Thanks for your reply.
> > I saw other posts about and if I understand good when O_DIRECT patches
> > will be in upstream loop driver the data loss risk will be solved, right?
> Stefano says that O_DIRECT is not needed, only correct barrier semantics
> are and he believes those are correctly implemented.
I not understand if manual changes and/or settings are needed, about 
this I mean:
> only correct barrier semantics are and he believes those are correctly 
> implemented
If yes what exactly?

> O_DIRECT would be an additional layer of safety perhaps, but sounds to
> be not strictly needed.
>
> Ian.

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