controlac
Contributor
Contributor

Software or Hardware iSCSI? No Jumbo Frame on HBA?

I was in the middle of planning to enable Jumbo Frame on my vSwitch and VMKernal's, all in the sudden I noticed from the GUI that I have 12 "Broadcom iSCSI Adapters" ready for use. I then found out the NIC's that came with our Dell PowerEdge R810 support iSCSI and those 12 iSCSI adapters were probably configured by Dell because we let Dell install VMWare at some extra fee.

Now both hardware and software iSCSI's are available to me, and I can choose either one to setup my SAN. I feel "hardware is always better than software", but I like to make sure that concept is right when applying in iSCSI.

I found out from "iSCSI SAN Configuration Guide" from VMWare, that all Broadcom adapters do not support Jumbo Frame, but that was a part that took me a lot of time digging into, while planning configuring my software iSCSI. If I chose HBA and lost the Jumbo Frame feature, do I need to concern about default MTU being too low (1500) and cause a performance degradation?

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4 Replies
IRIX201110141
Virtuoso
Virtuoso

If you open the dell case you'll see a small white dongle which enables the TCP Offloading and iSCSI Feature to the onboard nics. These nics acts as a "dependent" iSCSI HBA from the VMware view. Youre right that these HBAs doesnt support jumbo frames and IPv6.

Well... in most cases jumbo frames doesnt bring a better performance. Monitoring normal workloads for our EQLs (1GbE and 10GbE) together with some low level Open-E iSCSI solutions there isnt a big difference.

So dont worry about not using jumbo frames!

Regards

Joerg

'Remember if you found this or others answers helpful do not forget to award points by marking an answer as helpful or correct'

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controlac
Contributor
Contributor

Joerg,

Thanks for the reply. I think I can let go "Jumbo Frame" from my mind. But I am still undecided between using software iSCSI and HBA. I know either one will work fine but I still want to make the best choice to our environment.

Is it correct to say as long as HBA is an available option, we should always choose it over software based?

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cebomholt
Enthusiast
Enthusiast

It depends on workload I think whether or not you benefit from jumbos. As for always taking hardware, I wouldn't really argue with it other than saying you might be disappointed if you're expecting a significant performance boost. I found something similar a month or two ago where I had a HW initiator available on 3 hosts that were using software. After testing, I found performance to be the same. (benchmark iops/latency)

I'm guessing that if you have extra CPU available in your host, using the software initiator won't hurt anything- especially if it helps make your environment more consistent. Still, I have no good reasons why you shouldn't use the HBA features.

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controlac
Contributor
Contributor

Just for anyone who's interested in this same topic, I actually found a Reference that suggests using software initiator + Jumbo Frame should outperform HBA.

If his tests are truly unbiased, I guess I will use software base, looks like CPU usage shouldn't be a burden.

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