it is often cheaper to buy a spare of something and throw it in a cupboard rather than have a support contract.

I have a bunch of Aruba switches and this is what we do, because it's a lot cheaper.

If you are only buying a single spare that is the case. Support contracts make sense when you would want several dozen spares.

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dijit an hour ago | parent [-]

if a support contract is 70% of the cost of something, then for every 2 of something a spare is cheaper.

For Aruba I think it was 1:1; a support contract was the same price as the device itself over 2 years or something.

Support contracts never cover a "site" they always cover individual devices, so your cost scales with the amount you have... so I'm not sure I follow what you're saying..

Unless you mean to imply that you're replacing units more than once every 2 years, in which case of course you're right... but then I might consider going with another vendor entirely because that is a pretty terrible reliability record.

	▲	bluGill an hour ago \| parent [-]
		There are lots of different support contracts. Some of them really do cover the entire site. You seem to not realize the scale of a large data center. If every device lasts 5 years you are replacing 10 per day is not unheard of.