Also note that you can get the best of both worlds with a battery backed RAM cache contained in a SAN storage backend, such that the storage subsystem can be extremely low latency and yet "guarantee" that what it has accepted will get persisted to a disk for durability. (Predictably, this isn't cheap, but it's very effective.)
Your DB host tells the SAN to write this block, the SAN ingests the write to local RAM and reports "got it" to the DB server in sub-millisecond. The SAN will then dump that data to actual underlying discs over the next (hand-wavy) short timeframe, but from the DB's perspective, it got a durable fsync in under a millisecond.
Your DB host tells the SAN to write this block, the SAN ingests the write to local RAM and reports "got it" to the DB server in sub-millisecond. The SAN will then dump that data to actual underlying discs over the next (hand-wavy) short timeframe, but from the DB's perspective, it got a durable fsync in under a millisecond.