> is there any situation where you can actually get a sub-block short write on a disk or SSD device? Notwithstanding an inopportune time for power loss, or cer

> is there any situation where you can actually get a sub-block short write on a disk or SSD device? Notwithstanding an inopportune time for power loss, or certain other kinds of "hardware" failure, I'm not aware of any. And speaking O_DIRECT to the block device (as long as it's a real one, and not some network-mapped device, or loop) can indeed work well with a simpler protocol like the one you describe. That being said, I've had a lot of digs into file-based databases over the years, and I've never built a lot of confidence that those guys have any idea what they're doing: O_DIRECT or not. Usually it is application level, like an enterprise user trying to mix some performance suggestions with the database vendor and a storage vendor's own set of layers. The recent Postgres fiasco rather confirms that thinking, and suggests it doesn't even take something that complex going on to go wrong. However, more to the point: users of "XBlockFile" do not have any reason to believe the four-byte write is always going to be within the same sub-block, and there's absolutely nothing that can be done at the file-level to get that guarantee on UNIX (or to my knowledge: on Windows).