On Fri, Nov 15, 2024 at 03:05:21PM +0100, Mikulas Patocka wrote: > Note, that if a database uses buffered block device, performance will be > suboptimal, because the buffering mechanism can't create large bios, it > only sends page-sized bios. But that is expected to not be used - the > database should either use a block device with direct I/O or a filesystem > with or without direct I/O. And, as pointed out in the private mail that John forwarded to the list without my permission if we really have a workload that cares md could implement the plugging callback as done in md to operate on a batch of bios. Also not building large bios is not a fundamental property of block device writes but because it uses the legacy buffered head helpers. That means: a) the same is applicable to file systems using them as well b) can be fixed if someone cares enough, but apparently no one does
