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I traditionally build systems with 2 drives - a smaller drive for the system and a larger drive for storage (and backups).

I'm currently specing out a new system, and I'm trying to decide between a board with a 32 gb msata drive used for Intel Rapid storage/smart response and one without. The price differential isn't that large, though enough that I want to see some benefit to it, and there's other features in play here. I'm interested mainly in the effects having a small caching SSD would have on a system.

Would a caching SSD have any benefits to a system thats already booting off a reasonably fast SSD? I'm not talking raw speed - would it save on writes for example? Does the caching system also help with secondary drives like the storage one I want to use?

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Just to note i went with the board without. The answer makes sense, but if anyone can post an answer with citations , benchmarks or references, I'll likely switch the chosen answer to that – Journeyman Geek Feb 7 '13 at 9:54
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For reads:

In the ideal case, you have data being read from the cache SSD at the fastest possible speed, while simultaneously, data is being read from the "primary" SSD at the fastest possible speed. The throughput you could observe in this scenario is quite nearly the sum of the maximum throughput of the two drives taken together.

For writes:

Since the smaller SSD is only caching, any changes to pages in the cache have to eventually be written back to the primary storage media. There's no guarantee that the process of writing dirty pages from the caching SSD into the primary SSD would save writes or extend the lifespan of the primary SSD.

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