You can configure a drive to delay writing to the disk surface, and instead just write into its cache, until some later point when it's convenient to write the

You can configure a drive to delay writing to the disk surface, and instead just write into its cache, until some later point when it's convenient to write the surface. But the reason a DB issues a write to the disk is that the DB needs the data to be recoverable after a crash before the DB can proceed. So DBs cannot easily use the disk's write-to-cache feature; the disk's cache is no more durable than main memory. You might imagine that the disk would write-cache only an amount of data that it could write to the surface with the energy stored in its capacitors after it detected a power failure. But this is not the way disks work. Typical disk specs explicitly say that the contents of the write-cache may be lost if the power fails. You may be thinking of "tagged queuing", in which the o/s can issue concurrent operations to the disk, and the disk chooses the order in which to apply them to the surface, and tells the o/s as each completes so the DB knows which transaction can now continue. That's a good idea if there are concurrent transactions and the DB is basically doing writes to random disk positions. In the log-append case we're talking about, tagged queuing is only going to make a difference if we hand lots of appends to the disk at the same time. In that specialized situation it's somewhat faster to issue a single big disk write. You need to defer log flushes in either case to get good performance.