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Re: [libvirt] [PATCH v3 4/7] qemu: Translate the iscsi pool/volume disk source



On Wed, Jul 24, 2013 at 12:37:10PM +0200, Paolo Bonzini wrote:
> Il 24/07/2013 12:31, Daniel P. Berrange ha scritto:
> > On Wed, Jul 24, 2013 at 12:25:17PM +0200, Paolo Bonzini wrote:
> >> Il 24/07/2013 11:54, Daniel P. Berrange ha scritto:
> >>>> but anyway, we provide good enough documentations, so if one wants to
> >>>> use "direct" mode, he can still change the xml to use it, any big problems
> >>>> here? though defaulting to "direct" is more convenient for these users.
> >>>
> >>> Defaulting to "direct" is *NOT* more convenient for all users, only
> >>> those who happen to have a new enough QEMU, from a vendor who actually
> >>> decided to compile in the iSCSI support. If they're lacking such a QEMU
> >>> then the "direct" mode will prevent the default config from even starting.
> >>> This can never be an acceptable default choice. mode="host", while it huas
> >>> some limitations in features, is the only option that is capable of working
> >>> with any QEMU
> >>
> >> s/limitations in features/possibility of wreaking havoc to clusters/
> > 
> > This isn't a new issue. People have been using KVM with iSCSI in host
> > mode for as long as KVM has existed and the sky hasn't fallen in
> > clusters. As long as it is a documented limitation, that admins can
> > address with a config setting if desired, I don't see that this is
> > suddenly something we must fix at the cost of breaking the default
> > config for QEMU's without iSCSI support.
> 
> Understood, that's why I suggested not having a default config at all
> for type='lun' devices.

As I said before, that causes apps to have to do special handling
for iSCSI pools, which is not something we want.

> Also, can libvirt at least detect using a volume on a pool that wasn't
> started, and fail unless mode='direct'?

It should always fail to start the guest if the pool is not started,
regardless of the mode used.

Daniel
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