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.
--
Darren J Moffat
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