On Sat, Dec 26, 2009 at 11:00:59AM -0500, jim owens wrote: > Christian Kujau wrote: > > > I was using "sync" to make sure that the data "should" be on the disks > > Good, but not good enough for many tests... info sync > > CONFORMING TO > POSIX.2 > > NOTES > On Linux, sync is only guaranteed to schedule the dirty blocks for > writing; it can actually take a short time before all the blocks are > finally written. > > This is consistent with all the feels-like-unix OSes I have used. Actually, Linux's sync does more than just schedule the writes; it has for quite some time: static void sync_filesystems(int wait) { ... } SYSCALL_DEFINE0(sync) { wakeup_flusher_threads(0); sync_filesystems(0); sync_filesystems(1); if (unlikely(laptop_mode)) laptop_sync_completion(); return 0; } At least for ext3 and ext4, we will even do a device barrier operation as a restult of a call to sb->s_op->sync_fs() --- which is called by __sync_filesystem, which is called in turn by sync_filesystems(). This isn't done for all file systems, though, as near as I can tell. (Ext2 at least doesn't.) But for quite some time, under Linux the sync(2) system call will wait for the blocks to be flushed out to HBA, although we currently don't wait for the blocks to have been committed to the platters (at least not for all file systems). Applications shouldn't depend on this, of course, since POSIX and other legacy Unix systems don't guarantee this. But in terms of knowing what Linux does, the man page is a bit out of date. Best regards, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html