SanDisk has done something interesting with their new Extreme II SSD series, they have used both SLC and MLC flash in the drive to attempt to give users the best of both worlds.  The drive still has a DDR cache sitting between the flash storage and the controller, but there is an nCache between the MLC flash and the DDR comprised of ~1GB of SLC flash.  The idea is that the SLC can quickly accumulate a number of small writes into a larger single write block which can then be passed to the MLC flash for storage.  Don't think of it as a traditional cache in which entire programs are stored for quick access but more as a write buffer which fills up and then passes its self to the long term storage media once it is full.  The Tech Report put this drive through their tests and found it to be a great all around performer, not the fastest nor the best value but very good in almost any usage scenario.

"With MLC main storage and an SLC flash cache, the SanDisk Extreme II is unlike any other SSD we've encountered. We explore the drive's unique design and see whether it can keep up with the fastest SSDs on the market."

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