Auto-negotiation with Fibre Channel speeds

ORIGINALLY POSTED 31st May 2019

I had a recent question from within IBM regarding our support for auto-negotiation of Fibre Channel speed.

It seems we take this for granted, because we don’t specifically mention that all our Fibre Channel HBA’s across all the Virtualize family have supported auto-negotiate since our 4Gbit HBA back in 2005!

To be clear, across IBM Storwize V5000 series (all generations), IBM Stortwize V7000 series (all generations), IBM FlashSystem 9100 series and IBM SVC (since 8F4 nodes) the various Fibre Channel Host attachment interfaces will auto-negotiate with the switch to find the fastest commonly supported speed.

In general the Fibre Channel standards state N-2 so :

4Gbit -> will negotiate down to 2Gbit

8Gbit -> will negotiate down to 4Gbit and 2Gbit

16Gbit -> will negotiate down to 8Gbit and 4Gbit

32Gbit -> will negotiate down to 16Gbit and 8Gbit

Hope this helps to clarify for anyone looking for IBM’s official support for the above product ranges.

2 thoughts on “Auto-negotiation with Fibre Channel speeds

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  1. Is auto negotiation recommended or is it better to set fixed speeds? I found mixed opinions, some saying that, if possible, fixed / manual configured speed is better than leaving it auto negotiated…

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    1. I’ve not seen issues with auto negotiate for years. Occasionally a firmware level may have issues, usually when new speeds are just released, but generally should be all good. I have seen the odd case where a dirty optic results in failures to handshake at higher speeds.

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