This is my understanding as well, at least from reading the man pages. O_DIRECT and O_SYNC have different characteristics, so I'm a bit surprised at the responses here. Furthermore, using O_DIRECT over a 1Gbe connection yields 100-110MB/s performance where as O_SYNC on the same connection gives me around 20-30MB/s at best. There is definitely a difference. -Moazam On Sun, Nov 21, 2010 at 2:46 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Fri, Nov 19, 2010 at 04:26:35PM -0500, Trond Myklebust wrote: >> If the application requests O_DIRECT/O_SYNC or calls fsync(), we are >> required by POSIX to ensure the data is safe on disk. The presence of an >> NFS delegation does not change that requirement. > > That's not quite correct. O_DIRECT for one is not actually specific in > Posix at all, and the documented Linux semantics only say that the > pagecache should not be used (even if it sometimes is with various > filesystems). There is not guarantee that data actually is on disk or > reachable, for that you need to add the O_SYNC/O_DYSNC flag in addition > or use fsync/fdatasync. > > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
