On Wed, Aug 01, 2001 at 03:51:06PM -0400, Jeremy Impson wrote:
> On Wed, 1 Aug 2001, Jay R. Ashworth wrote:
> > If a drive fails in mid write, then there's *going* to be some data
> > half-written, no?
>
> Well, a journaling fs (as I understand it, 'natch), only guarantees a
> consistent file system (not safe data). That just means no need for
> exhaustive fsck.
That sounds much saner to me, but it does *not* sound to me like the
way that journalling filesystems are being pitched to suits.
> A journaling fs does this by writing out what it's about to do to a log,
> then doing whatever it said it was going to do (free blocks, create
> directory, move files). Afterwards, I think it also goes back to the log
> and says "OK" when it's done.
>
> If something fails when the log is being written, on reboot the equivalent
> of fsck looks at the log, sees it is inconsistent (but that I assume is a
> trivial check) and says "oh, the fs is OK".
Unless you force a full check -- which sometimes finds problems *anyway
-- yes.
> The difficult part is doing all this asynchronously. And quickly. This
> may be where journaling doesn't live up to its promise because it can be
> difficult to implement.
>
> I suppose a power spike could subvert a journaling fs (even a "perfect"
> one) if it causes the controller to return erroneous return values.
But you see, if the sales pitch is "journalling is worth the speed hit
because it protects your *data*", then they're lying. It only protects
your file system structures.
Cheers,
-- jra
--
Jay R. Ashworth [EMAIL PROTECTED]
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-- me
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