VMware ESXi 5.x - Delayed TCP Ack for iSCSI

Last Updated: 6/1/15

My HP StoreVirtual/LeftHand VSA storage system may be under performing due to delayed TCP ack. Not sure yet, but quite possibly is.

Thoughts:

I am starting to think this is how all ESXi deployments should be setup:

Regular Network Traffic: Delayed Ack On
iSCSI Network Traffic: Delayed Ack Off

Note: HP support suggested the following.

For HP SAN hardware: leave TCP delayed ack enabled.
For HP VSA SAN: disabled TCP delayed ack.

related webpages you should read:

Delayed ACK ESXi
http://helpthetech.com/2015/01/delayed-ack-esxi/

VNX iSCSI and TCP Delayed Acknowledgement - Thulin' Around
http://www.thulinaround.com/2012/12/17/vnx-iscsi-and-tcp-delayed-acknowledgement/

VMware KB: ESX/ESXi hosts might experience read or write performance issues with certain storage arrays
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1002598

VMware ESX/ESXi - TCP Delayed ACK - performance / congestion issues with iSCSI | Dell US
http://www.dell.com/support/article/us/en/19/SLN163743/EN

HP lefthand P4300 Storage write speed is too slow - HP Enterprise Business Community
http://h30499.www3.hp.com/t5/HP-StoreVirtual-Storage-LeftHand/HP-lefthand-P4300-Storage-write-speed-is-too-slow/td-p/5925011#.VTE0gpPfB_Y

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