4 ms·
The numbers in the post highlight an issue I have with Samsung consumer SSDs - they've slowed down FUA writes to an absurd degree. open_datasync
by anarazel 1y ago
The numbers in the post highlight an issue I have with Samsung consumer SSDs - they've slowed down FUA writes to an absurd degree.
open_datasync 249.578 ops/sec 4007 usecs/op
fdatasync 608.573 ops/sec 1643 usecs/op
open_datasync (i.e. O_DSYNC) ends up as FUA writes, fdatasync() as a plain write followed by a cache flush.
On just about anything else a single FUA write is either the same speed as a write + fdatasync, or considerably faster.
This is pretty annoying, as using O_DSYNC is a lot more suitable for concurrent WAL writes, but because Samsung SSDs are widespread, changing the default would regress performance substantially for a good number of users.