1 into 8 does not go!

Its easy to make a fool of yourself.
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?

Sadly all I did was break the port.   A port in Mod_Inv status means the SFP is in an invalid state.   This is not going to work.

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?

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About Anthony Vandewerdt

I am an IT Professional who lives and works in Melbourne Australia. This blog is totally my own work. It does not represent the views of any corporation. Constructive and useful comments are very very welcome.
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7 Responses to 1 into 8 does not go!

  1. Marcel Anthonijsz says:

    Yes, we still have some 1 Gbps connected SDLT tape drives for our customers, to restore old tapes at the BC&RS site in the Netherlands. We swapped out our F32 some time ago with a new B40 with 8 Gbps SFPs and encountered exactly the same problem. Feeding the B40 with Agilent SFPs did not work, luckily we did find a few 4 Gbps Brocade SFPs in another switch that were not used….

    • avandewerdt says:

      Thanks for the comment. Good to see I am not the only one who has been caught by this #;-) I was lucky to have a very helpful Brocade rep nearby. Once the 16 Gbps switches get more mainstream (which may take some time), we will have the same issue with 2 Gbps devices (which are also still quite common).

  2. Lukas says:

    Your post was very helpful today here in Brazil.
    Thanks.

  3. Oliver says:

    We have Brocade 300 for SAN switch and we ordered bunch a different SFPs single-mode LW and the result is funny. Pretty much half of them worked since brocade accepts only approved SFPs. Question is where can you find a supported SFP list for brocade 300?

    • With the 8 Gbps switches only Brocade branded SFPs work
      You will find some FInisar LW SFPs work because they need to allow long distance links to work esp CWDM links for which brocade don’t have SFPs themselves.

  4. Oliver says:

    Yes, Finisar was our only option. So whoever needs a small distance LW fabric with Brocade (i.e 300) go for Finisar. :)

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