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Re: [ts-7000] Solving the USB drive journalling issue please criticize

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Subject: Re: [ts-7000] Solving the USB drive journalling issue please criticize
From: "Don W. Carr" <>
Date: Tue, 19 Sep 2006 16:01:38 -0500
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. 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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