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

[Peter Lieven]

Am 28.04.2014 16:39, schrieb 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.

As written I am fine with lowering this to 4K.

Follow-Up or v3?

Peter

>
>>> 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