Thanks,
Robert
Stephen C. Tweedie wrote:
>
> Hi,
>
> On Wed, 14 Apr 1999 20:35:23 -0700 (PDT), George Bonser
> <grep@shorelink.com> said:
>
> > On Wed, 14 Apr 1999, Robert Kiesling wrote:
> >> > Notice how Linux writting to an ext2 file system is significantly faster
> >> > than any other OS/FS combination.
>
> > I think this is because when you time ext2 you are actually timing the
> > speed at which Linux writes to the disk BUFFER, not to the disk. The other
> > operating systems do not return from a write until the data is really on
> > the disk, if I remember correctly.
>
> Not true. Some other OSes (in particular, filesystems based on the
> FFS, Berkeley Fast File System) do use some synchronous writes, but
> only when creating and deleting files and only for the metadata, not
> the data itself. Synchronous data writes are only enabled if you
> explicitly ask for them (Linux included).
>
> The reason FFS uses synchronous metadata writes is not to give the
> application any on-disk consistency semantics (although the nature of
> the writes do imply at least some consistency guarantees), but to
> ensure that the order in which metadata structures are updated is
> predictable so that after a crash, the filesystem state can be
> recovered predictably. It does _not_ guarantee to recover your data.
>
> > ext2 returns nearly immediately. In other words, just because ext2
> > says the data was written to disk, it does not make it so in
> > reality.
>
> Just like for all of the other filesystems in question.
>
> Cheers,
> Stephen
>
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.rutgers.edu
> Please read the FAQ at http://www.tux.org/lkml/
-- kiesling@ix.netcom.com http://www.mainmatter.com/kiesling- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/