HDDs still have moving parts and SSDs still have no moving parts -- but reliability has gone from "SSDs less reliable" to "SSDs more reliable" over the past couple of years.
There are formulas and key specs to look at that allow you to figure out with fair reliability how long a drive will last.
But the bottom line with SSDs is, buy top-line drives (I like Intel's S3500s when I can get them). IMO, using consumer grade SSDs rather than enterprise grade is short sighted cost savings.
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