Its not hard to do.
All you is need is a moment of inattention combined with a massive assumption. In fact assumptions can bring you undone at any time. A former manager of mine introduced me to the saying: To assume is to make an ass of you and me.
So what was the assumption this time?
One of our business partners sold a client two new XIVs and 4 new IBM SAN40Bs (40 port fibre channel switches). So far so good. When you order the SAN switches you have a choice of ordering 4 Gbps capable SFPs (SFPs are the fibre optic sub assemblies that you plug your cables into) or 8 Gbps capable SFPs. There was a time when the 8 Gbps SFPs were much more expensive than the 4 Gbps, but today they are about 75% of the price of the 4 Gbps. So it makes sense to buy the faster SFPs. But you need to ensure that all the HBAs at the client site are at least 2 Gbps capable, because 8 Gbps SFPs are tri-rate and can only go at 2, 4 or 8 Gbps. Sure enough an assumption was made that this was not an issue... but it was. The client has WDMs that run at 1 Gbps and upgrading those WDMs would be a significant expense.
So I got to thinking... could I force the SFP to 1 Gbps?
If I display the 8 Gbps SFP it reports it is capable of 200, 400, 800 MBps which is code for 2, 4 or 8 Gbps.
But maybe I could force it to 1 Gbps?
So what to do? We could not just move the old SFPs into the new switch, as the new 8 Gbps capable Brocade switches only accept Brocade approved SFPs. The only solution was to make it right and swap four of the Brocade 8 Gbps SFPs with Brocade 4 Gbps SFPs. Fortunately as we needed only four, I was able to swap them with little expense or hassle (I contacted our local Brocade rep who happily helped us out).
The end point was a happy client and a lesson re-learnt..... 1 into 8 does not go.
I am curious though... is there much 1 Gbps gear still out there? Is this a common issue?