Don,
On Tue, 19 Sep 2006, Don W. Carr wrote:
> You guys should read the previous threads on flash, wear leveling, and
> journaled file systems. SD and other flash disks have load leveling built
> into the electronics. On board flash does need wear leveling, but many have
> electronics to do it, and thus can use VFAT without problems.
I think if you read my email that is a paraphrase of what I wrote :-)
I'm glad we are singing from the same hymn sheet.
Jim
> For maximum
> life many have recommended NOT using a journaled file system since you have
> extra writes. Though, if you have a big enough flash and only completely
> re-write it every month or so, no big deal, your flash will outlast the rest
> of the project by many years. Don.
>
> On 9/19/06, Jim Jackson <> wrote:
> >
> >
> >
> > .....snip....
> >
> > > > the
> > > > data to. You'll never know what flash controller, and even if you
> > > > did, I
> > > > understand many manufacturers don't even document what their
> > > > controllers
> > > > do. You have to trust that there's an internal capacitor and it stores
> > > > enough to allow the controller to complete the write even if the
> > > > stick is
> > > > pulled at the most inopportune moment.
> > >
> > > Hmmm.... there's a scenario I didn't count on. Do the SD cards suffer
> > > from the same fate ?
> >
> > I don't know for sure, but any flash memory will need a controller. And
> > I'm fairly certain they'd have to build in some wear-levelling algorithms,
> > faulty block testing substitution etc otherwise with FAT filesystems the
> > blocks used for the main directory will wear out PDQ.
> >
> >
> > > >
> > > > I wish you well. If you have time I'd be interested in an outline of
> > what
> > > > you end up doing and how it performs in practice.
> > >
> > > By the sounds of it whatever I do will have random results...
> >
> > In that case, if the data is really valuable then your customer will have
> > to accept more stringent procedures for removal. If the loss of the most
> > recent set of data is not that important, then it doesn't really matter.
> >
> > I have heard of tales of the whole card (CF) being made inoperable and no
> > data recovery possible, but not sure how much is urban myth, user
> > problems, or just misreporting. That's why I'd be interested in practical
> > experiences.
> >
> > I've never had CF problems with my ts7200, and I've crashed it, accidently
> > pulled the power lead and done all sorts of odd stupidities (I run the OS
> > from an installed CFdisk). My CFdisks are cheap ones.
> >
> >
> >
>
>
>
> --
> Dr. Don W. Carr
> J. G. Montenegro 2258
> Guadalajara, Mexico
> +52-333-630-0704
> +52-333-836-4500 ext 2930
>
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