Truenas 12 Core Iscsi write performance very slow

[lucadaniele]

Hi everyone, I have been using freenas for a long time now as iscsi san for my Esxi 6.2 infrastructure with excellent results. I use three gigabit interfaces only for iscsi traffic to esxi hosts configured on three subnet in multipatching mode(round robin). After I upgraded my systems to truenas 12 core, the write performance on storage are deteriorated. Both before and after the zvol upgrade. Someone knows if it is a known problem and if there is a solution?
My Freenas storages runs on tree dell t5500
Intel(R) Xeon(R) CPU E5530 @ 2.40GHz
48 Gb Ram ECC
Pool/Zvol over tree SSD Samsung 850 evo 2Tb RaidZ1 (lz4)

I am attaching the images of a single Vm performance before and after the upgrade

Thanks to anyone who can help me
Luca