On Fri, Feb 05, 2016 at 03:25:00PM -0700, Ross Zwisler wrote: > According to the standard specification (e.g., POSIX.1-2001), sync() > schedules the writes, but may return before the actual writing > is done. However, since version 1.3.20 Linux does actually wait. > (This still does not guarantee data integrity: modern disks have large > caches.) > > Based on this I don't believe that it is a requirement that sync and syncfs > actually flush the data durably to media before they return - they just need > to make sure it has been sent to the device, which is always true for all > writes PMEM via DAX, even without any calls to dax_writeback_mapping_range().
For Linux there is a requirement to not return before the data is on disk, and our users rely on it. The man page is rather confusing, and I'll see if I can fix it up.
