ESXi freezes when storage over ISCSI to Synology times out during high load

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I have a Fujitsu RX 300 S7 with ESXi 6.0 U3 and a Synology RS2416+ containing a RAID 10 with 4x 4 TB WD Red HDDs. I have created a file-based LUN on the Synology and I have connected the Target to the ESXi over 3 NICs via round-robin. This means, that all of the 3 NICs are used for the connection between the ESXi and the Synology (I have followed this tutorial).


I have made several tests with WMware IOMeter and CrystalDiskMark and the results are great (350 Mb/s and ~50k IOPS read), but during the tests, the ESXi hypervisor freezes. If I disable the Target on the Synology and enable it back again, the ESXi and the test VMs start working as if nothing had happened.


In the vmkernel.log I can find find several entries containing this line: “Waiting for timed out HB” (please find a screenshot attached)


Whan is the cause of the error? How can I fix the timeouts? I really need the higher throughput (=3 NICs) for better performance.


Thank you in advance!


Kind regards,


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