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iSCSI - Offload or Jumbo Frames

Posted on 2013-10-24
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Last Modified: 2013-11-18
Dear Experts,

I have purchased a HP 530T card (1Gb), which is a hardware iSCSI card with TOE.
I planned to use the offload capability with jumbo frames but according to KB article 1007654

"You cannot use Jumbo Frames on a Broadcom card that is configured as a hardware initiator performing iSCSI Offload functions. You can either use Jumbo Frames or iSCSI Offload and you cannot use both together with the Broadcom adapters."

im not sure what config to go with

1) HP 530T Card HBA (switch off offload) and use jumbo frames
2) HP 530T Card HBA with offload but no jumbo frames.

Has anyone done any benchmark test with offload vs jumbo rames. Any advise on the route I should take?

Thanks in advanced
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Question by:Rio_10
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LVL 119
ID: 39596550
In our experience, we have found the "in-built" iSCSI Software Adaptor, and the use of Jumbo Frames outperforms Hardware iSCSI Initiators, which cannot use Jumbo Frames.

This would appear to be the general consensus.

http://www.vmadmin.co.uk/resources/35-esxserver/252-esxihwswiscsijumbo

If you have the ability to use Jumbo Frames it's always recommended to test, if your SAN, and Storage Switches support Jumbo Frames, and have enough buffer space in the physical switches to support such actions.

Mileage will vary, to say, your network and site, may be different to ours, and therefore we would recommend you conduct your own tests, and reach a conclusion.

On some configurations, we have seen jumbo frames, making performance worse.

Jumbo Frames can overcome read and write latencies, when the datastores are being maxed out.
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Author Comment

by:Rio_10
ID: 39596662
Jumbo Frames can be used on hardware Initiators.

"Jumbo Frames for all iSCSI adapters in vSphere 5.1 and vSphere 5.5 can be configured using the UI. This applies to Software iSCSI,Dependent Hardware iSCSI and Independent Hardware iSCSI adapters"

I will test but it looks like i will disable the TOE and use jumbo frames. My switches also support jumbo Frames.

My storage has 8 ports, 4 on each controller. I have 4 ESXi HBA ports, I have read some conflicting info regarding 1:1 mapping.

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2038869

Do I configure the following

vSwitch1 - 192.168.0.1 --> Physical switch --> Controller 1 192.168.0.201
vSwitch2 - 192.168.1.1 --> Physical switch --> Controller 2 192.168.1.201
vSwitch3 - 192.168.2.1 --> Physical switch --> Controller 1 192.168.2.201
vSwitch4 - 192.168.3.1 --> Physical switch --> Controller 2 192.168.3.201

Physical switch --> Controller 1 192.168.0.202
Physical switch --> Controller 2 192.168.1.202
Physical switch --> Controller 1 192.168.2.202
Physical switch --> Controller 2 192.168.3.202
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Accepted Solution

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Andrew Hancock (VMware vExpert / EE MVE^2) earned 500 total points
ID: 39596718
Not ALL iSCSI Hardware initiators, can do JF.

If you want to do multipath...

see my EE Articles

HOW TO: Add an iSCSI Software Adaptor and Create an iSCSI Multipath Network in VMware vSphere Hypervisor ESXi 5.0

do you only have a single physical switch?
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Author Comment

by:Rio_10
ID: 39596837
I have two Physical switches.
I read that How to but that means that all the iSCSI ports on the SAN (8 of them) neet to be on the same subnet.

This is where the conflict is. The SAN manufacturer state to use different subnets on its ports but but VMware states no too.

VMware states to use 1:1, one vSwitch to one pNic if its on different subnets.

or am I just being OTT. Shall I Just put all the host iSCSI and SAN ports on the same subnet
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LVL 119
ID: 39597042
Same subnet or different subnets, depends how complex you want to make it, you will still have multiple paths to the Storage.
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