Re: [Qemu-devel] [PATCHv2 RESEND] block/iscsi: speed up read for unallocated sectors

[Paolo Bonzini]

Il 28/04/2014 15:43, Peter Lieven ha scritto:
> > b) the allocationmap should be allocated even for out-of-range opt_unmap_gran, 
> > using a granularity of 64 sectors in that case.
>
> Would the increase of the resolution bring any benefit? If we increase the 
> resolution I think all sectors falling into the same
> physical cluster would end up with the same status.

What if opt_unmap_gran is 32K or lower?  In this case you're not using 
an allocationmap.

> > c) an opt_unmap_gran of 32K should be used by QEMU as a cluster size
>
> Do we have evidence of used cluster sizes on real hardware? I only know our 
> Equallogic storages which have 30720 sectors.

IDE does not specify the granularity, so an IDE disk will show a 
granularity of 1 sector (but it has LBPRZ=0).

> > d) the threshold should be dynamic and equal to iscsilun->cluster_sectors
>
> I don't think this is useful. For big cluster_sizes we will end up to never use 
> the allocation cache.

Right.

Paolo