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Hey Markus,
thanks for the Benchmark.
I did some experiments too and i still think there is a nfs bottleneck and in my opinion your bench proof it.
Today i copied my vm to local sas discs and see the snapshot creation of the vm with 8 gb ram tooks less than 4 minutes.
After this test i copied the vm back on nfs now just with a gbit link and again 8 minutes.
Its not a real bottleneck but it does not make sense that if i create a snapshot on 2 local raid one discs it takes less than 50% of the time as if i do on a 10gbit connected empty host nfs with 20 discs.
Especially is nfs sata or sas does not make a difference and 10gbit or 1 gbit does not change anything.
it is like you say no bottleneck it must be something deep in the nfs stack with the snapshot api. Because if i do storage vmotion i can copy 100GB of data on the same store in round about 10 minuets and on the other hand 8 GB Memory contend of an idle machine takes nearly the same amount of time.
Maybe ill open a support case now that i talked with you and checked for missconfiguration just to clarify what performance is expected and why nfs is so slow compared to local discs.
Or i just try another nfs targed or iscsi to cross check.
Thanks for your awesome support and i will let you know if i can figure it out finally if it is a normal behaviour or just weired nfs stuff.