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=== Solid State Disks ===

These are very fast disks, and if you build an array from them, you are best off using raid-1 (mirror). This is a scenario where using the other forms of redundant raid (ie 5 or 6) is actually likely to slow access down!

A new facility (2016) of raid is to use an SSD as a journal. [TODO: Improve my understanding of journalling] This flushes writes to the SSD, partly to speed the system up for the user, and partly to optimise writes to slower rotating media, as it allows changes to accumulate in the journal until a full stripe can be flushed to rotating media in one go.