On 01/07/2011 01:15 PM, Darren J Moffat wrote:
> On 07/01/2011 11:56, Sašo Kiselkov wrote:
>> On 01/07/2011 10:26 AM, Darren J Moffat wrote:
>>> On 06/01/2011 23:07, David Magda wrote:
>>>> On Jan 6, 2011, at 15:57, Nicolas Williams wrote:
>>>>
>>>>> Fletcher is faster than SHA-256, so I think that must be what you're
>>>>> asking about: "can Fletcher+Verification be faster than
>>>>> Sha256+NoVerification?"  Or do you have some other goal?
>>>>
>>>> Would running on recent T-series servers, which have have on-die
>>>> crypto units, help any in this regard?
>>>
>>> The on chip SHA-256 implementation is not yet used see:
>>>
>>> http://blogs.sun.com/darren/entry/improving_zfs_dedup_performance_via
>>>
>>> "Note that the fix I integrated only uses a software implementation of
>>> SHA256 on the T5120 (UltraSPARC T2) and is not (yet) using the on CPU
>>> hardware implementation of SHA256.  The reason for this is to do with
>>> boot time availability of the Solaris Cryptographic Framework and the
>>> need to have ZFS as the root filesystem."
>>>
>>> Not yet changed it turns out to be quite complicated to fix due to
>>> very early boot issues.
>>>
>> Would it be difficult to implement both methods and allow ZFS to switch
>> to the hardware-accelerated crypto backend at runtime after it has been
>> brought up and initialized? It seems like one heck of a feature
>
> Wither it is difficult or not depends on your level of familiarity
> with ZFS, boot and the cryptographic framework ;-)
>
> For me no it wouldn't be difficult but it still isn't completely trivial.
>
>> (essentially removing most of the computational complexity of dedup).
>
> Most of the data I've seen on the performance impact of dedup is not
> coming from the SHA256 computation it is mostly about the additional
> IO to deal with the DDT.   Though lowering the overhead that SHA256
> does add is always a good thing.
>
Well, seeing as all mainline ZFS development is now happening behind
closed doors, all I can really do is ask for features and hope Oracle
implements them :-). Nevertheless, thanks for the clarification.

BR,
--
Saso
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