Redundancy and Failure

We’ve all encountered failure at some point in our lives. I write this thinking about failure in the equipment that we use to take our images. In particular I’m looking at the aspect of redundant storage cards in a camera vs the system as a whole – and providing some thoughts for you to take away.

Many of the higher end mirrorless and DSLR cameras are providing two slots for either SD or CF cards and the option to write out to both cards at once. This is seen quite rightly as the classic case of good redundancy to guard against card failure… and here is where we get to some detail.

Firstly the lifespan in number of writes that one leading manufacturer quotes is around 100,000 – that is writing once a day to the whole card for 270 something years will eventually wear the card out. So let’s assume at the outside they only last 10% of that – that still 27 years of daily work. So we hear the stories of photographers that experienced card failure in a year or two of writes a few times a week. The summary of these failures tends to be like: a statistical significance of failure of several cards at 200 writes into 100,000 write lifetime. Compare this failure scenario with the multitude of mobile phones, IOT, network, PC’s and servers that write to the same SSD technology for years on end with extremely low failure rates.

This is where we see a logical failing – why should one application of the same storage inside a camera result in grossly poor reliability? Why when we see this reliability issue are we blaming the storage technology rather than another aspect unique to digital photography?…  We shouldn’t rush to blame the card against all logic because it’s at the mercy of unique external forces – batteries going flat, cards being ejected while being written to, salty sweaty pockets and a lot more.

But some say a redundant card will fix this. Two cards at the same time equally are at the mercy of flat batteries, card doors opening and being ejected while being written to, salty sweaty pockets. From the analysis above, they still are inside a device with demonstrable history of making cards fail early in life. Here’s where we start to discover the difference the difference between redundancy and the risk of failure.

The easiest way to see this is with an analogy – very few multiple engine planes crashes happen due to both engines failing. Think about that…carefully. A lot of crashes are bad judgement, bad weather, bad engineering and so on. The moment the plane crashes one or two of the engines are usually perfectly fine and running reliably – but still all is lost.

By all means I’ll allow you to be suspicious of the reliability of one solid state encapsulated microchip – add a second different model as a redundancy if you wish. But the risk here is focussing on those two cards rather than the dozens of switches, electro mechanical mechanisms, connectors, apertures, focus motors, cables, batteries, displays, shutters, humans… that make up the entire single camera system.

Keep your mind open to the risk of only having a single body with you. Think about thieves, drops, one bag with all your kit next to the water, single lenses with no alternative, no insurance. If you understand the risks and mitigate all key things – that will be your true redundancy and reliability.

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