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

[Paolo Bonzini]

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.

> 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.

Paolo