> I know it is often a design choice for some system vendors to > say they are posix compliant while not meeting the data > integrity requirements just so they can win benchmarks. They > don't document it, they hope they never get caught. Or do you > think the specs don't require data to reach non-volatile storage? Saying you're POSIX compliant isn't a design choice; it's a marketing choice. But I do think POSIX doesn't require data to reach the platter. I looked into this a while back when I was designing a filesystem type that had lots of levels of data stability and found that POSIX is intentionally ambiguous about what fsync means. Its words are "stable storage." Stability is relative. That the data can't disappear if the OS crashes is one important kind of stability. Even data on the platter is not perfectly stable, as data has been known to be not retrievable from a platter. Electronic storage can be as stable and non-volatile as magnetic media with a good enough UPS. But all that is kind of irrelevant, because users don't want POSIX compliance; POSIX is just a word. If the user wants a system where a storage device power failure doesn't cause data loss, he needs a certain fsync behavior. If he wants one where he can do N transactions a second on a single disk drive and doesn't have a risk of storage device power failure, he might need a different fsync behavior. I don't know if filesystem driver or storage device vendors are intentionally misleading customers about how stable the storage is; it doesn't seem like something one could get away with, considering who buys these. But I do know there's plenty of misunderstanding, and that's bad. -- Bryan Henderson IBM Almaden Research Center San Jose CA Filesystems -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
