ESXi iSCSI write speed drops when using Multipath IO

Hi all,

I’m using a Synology Diskstation DS1512+. Both network interfaces are connected to a different switch, different VLANs and have addresses in different subnets. In ESXi 5.5 I have 2 interfaces for iSCSI, each in one of the subnets and connected to the same switch as the interface interface of the Synolgy device.

When I use 1 path for storage the read and write speeds max out at nearly 125 MB/s which is the maximum for my gigabit connection. I get the same result no matter which of the 2 paths I use.

When I use round robin and use both paths at the same time my read speed goes up to around 170 MB/s but my write speed drops to 80 MB/s.

What am I doing wrong?

Thanks in advance for you answers & suggestions