On Mon, 16 May 2011, walter marvin wrote:
> Some devices may have advanced wear levelling techniques. But OS' tend to
> write meta data in the same place, so that's what wears out first.
No. Because wear levelling is basically a technique that maps the block the
OS _thinks_ it is writing to (the logical block number) to a real physical
flash block. Thus allowing the physical block used to be moved around the
device to level the write wear.
> Solution: Journaling.
This is a non-sequitor.
Can I suggest you read up on what wear levelling actually means?
Try the Wikipedia article at
http://en.wikipedia.org/wiki/Wear_leveling
Then try this from an actual manufacturer...
http://download.micron.com/pdf/.../nand/tn2942_nand_wear_leveling.pdf
I'm sure google will throw loads of extra articles/papers.
> On Sun, 15 May 2011, walter marvin wrote:
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> > It the writes per cell that is the limit not total writes journaling will
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> > repair a cell that has had too many writes
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> Yes but misleading. All flash based devices like USB sticks and SD cards,
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> CFdisks etc contain wear levelling. Where the journal is stored will move
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> about the flash blocks to spread the wear out.
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> I repeat, increasing the total number of writes to the flash devices
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> increases the wear on the flash memory. Whether this is important in one's
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> application is upto the engineer to determine. Just ignoring it with bland
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> platitudes is not sensible engineering.
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> > --- On Sun, 5/15/11, Jim Jackson <> wrote:
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> > From: Jim Jackson <>
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> > Subject: Re: [ts-7000] TS-7553 MicroSD longevity
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> > To:
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> > Date: Sunday, May 15, 2011, 5:27 PM
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> > On Sun, 15 May 2011, walter marvin wrote:
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> > > My info is infinite reads but limited writes this means that you must use
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> > > a journaling file system or build in track remapping
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> > Not sure that makes sense. In fact a journalling file system INCREASES
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> > writes - first to write the update details to the journal, then to
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> > do the updates, then the make the update done in the journal.
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> > The use of a journalling file system helps if the system is likely
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> > to suffer unexpected power loss etc. When it comes back up, any uncompleted
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> > transactions can be verified and completed, and there is usually no need
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> > for a very lengthy file system integrety check.
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> > As an engineer it's up to you decide the trade offs and decide which is
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> > more important. My own systems have battery backup, allowing graceful
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> > shutdown, so I use ext2 (mounted with "noatime") to reduce writes. If I
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> > didn't use battery backup, I'd use ext3, and stand the write hit to give me
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> > > --- On Sun, 5/15/11, parkranger_dan <> wrote:
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> > > From: parkranger_dan <>
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> > > Subject: [ts-7000] TS-7553 MicroSD longevity
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> > > To:
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> > > Date: Sunday, May 15, 2011, 1:37 PM
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> > > Hey guys. I posted awhile back when having some functionality
> > > issues with a TS-7200 and realized the 7553 was really the platform I
> > > should have been working with from the get-go.
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> > > Sweet little box this 7553. I've gotten all my software ported over and
> > > it's working perfect. After only a couple weeks with it, I think I'm
> > > ready for deployment.
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> > > We'll be preparing quite a few of these little guys. Having the ability
> > > to insert a pre-imaged MicroSD, set one jumper, and run one command (rm
> > > linuxrc; ln -sf /linuxrc-sdroot /linuxrc; save) to change the boot is
> > > very attractive in terms of quick deployment, and easy field upgrade
> > > (send customer a new MicroSD card, done!).
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> > > One question I had was in regard to the longevity of these little MicroSD
> > > cards, and their resilience to repeated power loss.
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> > > Customers will not have the ability to shutdown nicely, power will always
> > > be removed to turn off. I based my image from the latest.dd image
> > > available from the Technologic website, which if I remember correctly is
> > > formatted ext3.
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> > > Has anyone had any experience with a similar setup? How are the boxes
> > > holding up, and have the MicroSD cards been lasting?
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> > > I've been also pondering making use of the xnand drive with a custom
> > > busybox that includes the compiled apps i need and just script the
> > > flashing process to ease prep/deployment. I know bootup time would be
> > > significantly better than my current 1 minute timeframe, and resilience
> > > would be better. Downside would be that I lose the ability to do remote
> > > software updates. Anyway, I have yet to break ground on that idea, or
> > > even wrap my brain around how that's done.
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> > > Thanks!
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> > > Dan
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