Re: [Qemu-devel] [PATCH] block/iscsi: use 16 byte CDBs only when necessary

[Peter Lieven]

On 17.06.2014 13:46, Paolo Bonzini wrote:
> Il 17/06/2014 13:37, Peter Lieven ha scritto:
> > On 17.06.2014 13:15, Paolo Bonzini wrote:
> > > Il 17/06/2014 08:14, Peter Lieven ha scritto:
> > > > >
> > > >
> > > > BTW, while debugging a case with a bigger storage supplier I found
> > > > that open-iscsi seems to do exactly this undeterministic behaviour.
> > > > I have a 3TB LUN. If I access < 2TB sectors it uses READ10/WRITE10 and
> > > > if I go beyond 2TB it changes to READ16/WRITE16.
> > >
> > > Isn't that exactly what your latest patch does for >64K sector writes? :)
> >
> > Not exactly, we choose the default by checking the LUN size. 10 Byte for
> > < 2TB and 16 Byte otherwise.
>
> Yeah, I meant introducing the non-determinism.

Ah okay :-)

> > My latest patch makes an exception if a request is bigger than 64K
> > sectors and
> > switches to 16 Byte requests. These would otherwise end in an I/O error.
>
> It could also be split at the block layer, like we do for unmap. I think there's 
> also a maximum transfer size somewhere in the VPD, we could to READ16/WRITE16 if 
> it is >64K sectors.

That would be an idea. I will have a look.

Peter

> Paolo


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Peter Lieven

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