For a high-valued production data, if you think your data is safe after it's (finally) written to disk, then you're doing it wrong. Your data is not safe until

For a high-valued production data, if you think your data is safe after it's (finally) written to disk, then you're doing it wrong. Your data is not safe until a) it left the physical database machine, b) it left the physical datacenter to be stored into multiple datacenters around the world (e.g. S3). Thus ideally, the (horribly slow) disk doesn't even come into play, especially for in-memory DBs. You buffer the data in memory before they are sent out of the machine/datacenter, but you make sure to mirror this buffer at multiple separate physical machines (which your database cluster should support), in case one goes down or over. Once the data are committed into a replicated store, you can clear that buffer. Fast and reliable. This is not to say that there are zillion cases where harddrive is still the ideal persistence device. After all, it's very hard to destroy a harddrive in a way to make the data unrecoverable (of course, I'm talking about cases where RAID failed or wasn't present). However in reality, data from broken harddrives are seldom attempted to be recovered, mainly I guess due to the price and relatively long service waiting times.