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.
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.
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 atSimply-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.