Re: document ext3 requirements

Pavel Machek
2009-01-04T22:23:34Z

On Sun 2009-01-04 17:06:34, Theodore Tso wrote:
> On Sun, Jan 04, 2009 at 01:49:49PM -0600, Rob Landley wrote:
> >
> > Want to document the granularity issues with flash, while you're at it?
> >
> > An inherent problem with using flash as a normal block device is that the
> > flash erase size is bigger than most filesystem sector sizes. So when you
> > request a write, it may erase and rewrite the next 64k, 128k, or even a couple
> > megabytes on the really _big_ ones.
> >
> > If you lose power in the middle of that, ext3 won't notice that data in the
> > "sectors" _after_ the one your were trying to write to got trashed.
>
> True enough, although the newer SSD's will have this problem addressed
> (although at least initially, they are **far** more costly than the
> el-cheapo 32GB SD cards you can find at the checkout counter at Fry's
> alongside battery-powered shavers and trashy ipod speakers).
>
> I will stress again, that most of this doesn't belong in
> Documentation/filesystems/ext3.txt, as most of this is *not*
> ext3-specific.

I've initially done the patch for ext3 because that's what I'm using
and becuase I felt responsible for documenting it after a huge thread.

At least barrier=1 seems to be ext3 specific, and perhaps logfs or
something can survive full eraseblocks disappearing. Anyway, i guess
we all agree that this needs to be documented _somewhere_, and that's
what I'm trying to do.
Pavel
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