Comment by shivak
4 years ago
As you noted, Apple's fsync() behavior is defensible if PLP is assumed. Committing through the PLP cache isn't how these drives are meant to operate - hence the poor behavior of F_FULLSYNC.
But this isn't specific to Macs and iDevices. Some non-PLP drives also struggle with sync writes on FreeBSD [1]. Most enterprises running RDBMS mandate PLP for both performance and reliability. I understand why this is frustrating for porting Linux, but Apple is allowed to make strong assumptions about how their hardware interoperates.
[1] https://www.truenas.com/community/threads/slog-and-power-los...
There is no PLP. If you yank power you lose up to 5-10 seconds of disk cache (fsynced files that weren't F_FULLFSYNCed). I tested this. On macOS.
I guess we expected a marvelous interplay of hardware and software, but all we got was fudged numbers.