Re: sync & asyck i/o

Stephen C. Tweedie (sct@redhat.com)
Tue, 6 Feb 2001 17:34:37 +0000


Hi,

On Tue, Feb 06, 2001 at 02:52:40PM +0000, Alan Cox wrote:
> > According to the man page for fsync it copies in-core data to disk
> > prior to its return. Does that take async i/o to the media in account?
> > I.e. does it wait for completion of the async i/o to the disk?
>
> Undefined.

> In practice some IDE disks do write merging and small amounts of write
> caching in the drive firmware so you cannot trust it 100%.

It's worth noting that it *is* defined unambiguously in the standards:
fsync waits until all the data is hard on disk. Linux will obey that
if it possibly can: only in cases where the hardware is actively lying
about when the data has hit disk will the guarantee break down.

--Stephen
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/