Poor SMB Performacne

[VSprague]

I have an ESXi 6 host with an iSCSI Raid 10 NAS for storage. I also have a Hyper-V host running with a VM on the same the host. I've been testing SMB File transfer performance between guest VM's. What I'm running into is when copying large files to and from guest VM's on the VMware host after about 2GB the file transfer slows down from 110MBps to around 45-50MBps. This issue does not occur on the Hyper-V guest VM so I know it's not a hardware issue. The guest VM's are also all Server 2012 R2.

[vijayrana968]

What is model of NAS is in use, if it is working fine on Hyper-V then there must be configuration issue in ESXI configued settings. Have you enabled Jumbo Frames !

[VSprague]

Yes, jumbo frames are enabled. I have 4 gb nics on the host and 4 on the NAS. All IP'd separately. Multipathing is also enabled and functioning. It's a Synology DS1815+ with 8 Western Digital 5tb Red Pro drives.

*Edit - I also dropped the IOPS Round Robin limit down to 1 which helped a little in overall performance but has not addressed this issue.

[VSprague]

So after some additional testing I noticed something else odd. If I drop the number of NIC's assigned to the iSCSI software adapter down to 2 from 4 the issue goes away. Not sure why that happens but that seems to be the case. I'm experimenting with different number of NIC's and I'm going over the vmkernel log.

[VSprague · Accepted solution]

So I was doing more testing and actually raising the IOPS Count for Round Robin to 100 actually resolved the SMB performance. However I'm still seeing an issue with Round Robin and it doesn't want to us more than 120mbs between all 4 nics. I've read a few things my understanding was with round-robin I should be able to fully utilize all 4 nics but currently I can't.

[VSprague]

So I determined that with iSCSI Round Robin ESXi will not use more than 1 NIC worth of throughput which is why I was limited to the 120mbps transfer speeds.