O_DIRECT doesn't provide power-cut durability on storage devices with write cache.
Recently written and acknowledged data can still be lost on a power cut.
You still need fsync, fdatasync or equivalent after an O_DIRECT write, to tell the storage device to commit its write cache to the non-volatile layer.
(And last time I looked, I think some filesystems even incorrectly failed to flush the device write cache on fsync after O_DIRECT writes because of no dirty page states.)
There’s a ton devices on the market that would lie to you too saying caches are flushed while they aint. If you really want that data to be there better use “server grade” hw with power loss protection
Recently written and acknowledged data can still be lost on a power cut.
You still need fsync, fdatasync or equivalent after an O_DIRECT write, to tell the storage device to commit its write cache to the non-volatile layer.
(And last time I looked, I think some filesystems even incorrectly failed to flush the device write cache on fsync after O_DIRECT writes because of no dirty page states.)