Space efficiency of a different kind

When your buying a car it’s worth opening the boot (that’s the trunk for my American friends) and looking at the spare to see what kind it is.  Car manufacturers sometimes choose to sacrifice a full spare to save space (or cost). I can understand the motivation, but there is nothing worse than having a flat and then finding that your spare is half the tyre you expected it to be.

With low end fibre channel switches there is a similar challenge when working to achieve the lowest cost and smallest footprint in a 1U form factor.  The main way it expresses itself is with power supplies.

The IBM SAN24B-4 (a 24 port switch) is a case in point as it only has one fixed power supply.   This of course means that if that power supply fails, then that switch will be down and the entire unit will have to be replaced.  If you have dual fabrics (two switches) with dual pathed hosts, then this should not cause an application outage, but it may not be what you expected.  You also need to ensure that each switch is connected to a different power rail (and/or UPS) to cater for building power issues.

IBM SAN24B-4 with power supply highlighted

How to avoid this?   Purchase the slightly larger IBM SAN40B-4 (a 40 port switch) which comes with two hot swap power supplies as standard.   It’s a little more expensive (which makes sense as it has more ports and more hardware) but also offers redundant power and greater scaleability.

IBM SAN40B-4 Front View

IBM SAN40B-4 with one power supply being removed

Of course in the end you need to select the switch which matches your budget.  The SAN24B-4 starts at only 8 ports active while the SAN40B-4 starts at 24 ports active, so the SAN24B-4 will always be a cheaper purchase.   The SAN24B-4 is also much smaller, lighter (it weighs 4.35 kg versus 9.34 kg) and uses less power (48 W versus 84 W).

My preference?  Well I would always choose to use a switch with dual redundant hot-swappable power supplies, but then I am not the person signing the cheques.   What I would suggest is that if you choose the SAN24B-4 then you need to ensure your backing up your switch config (especially if your running single switch fabrics).  You could look at Simply-Save-Your-SAN as one way to do this.

And no… that is not my car.   By shear synchronicity I was thinking about this issue when I spotted this car in the carpark at Southgate.  Timing is everything.


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.
This entry was posted in Brocade, SAN and tagged , , , , . Bookmark the permalink.

5 Responses to Space efficiency of a different kind

  1. Jim says:

    I avoided B24’s for a quite a while after they came out because of this. As the owner of a Suzuki Swift Sport I can raise you one on the spare tyre (clearly that’s a non-sport model you have in your picture). The Sport has a larger engine and twin exhausts among other things and consequently no room for a spare of any kind! So I carry a canister of tyre foam to cover the eventuality that a tyre goes flat one day. 3 years so far with no need to use it. It made me uneasy for a while, but I got over it – both the tyre thing and the B24 thing. Maybe that’s the message, maybe the power supplies on the B24 have a very low failure rate and the risk is manageable, especially in dual fabrics.Maybe everything has its compromises and it’s just a question of calculated risks.

    • avandewerdt says:

      Hi Jim.
      Thanks for the comment.
      Totally agree with what you say, the risk is quite manageable and a great many customers are happily running their SANs on B24s.
      My main concern is that they clearly understand the difference and that they make a well informed decision based on it.

  2. Pingback: Space Efficiency of a Different Kind - The Business of IT Storage Blog - IBM Storage Community

  3. Alan says:

    The space saver spare is all cost, tyre manufacturers give them away to car manufacturers. All to make you buy 2 tyres rather than one when you first wear them out.

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