Flash File System Concerns

[Gary D. Thomas]

On Fri, 2003-03-28 at 10:11, Prakash kanthi wrote:
>
> Folks,
>
> I have one concern regarding FFS. If you use flash for
> your entire filesystem including /var/log, /proc,
> etc.., you will be accessing flash too many times.
>
> And there is good chance that, your flash on the board
> reaches maximum number of accesses/writes limited by
> flash technology.
>
> How do people generally handle that in the industry.
> Especially, if you have on-board (non-replaceable)
> flash?
>

First of all, use a proper FLASH file system (like JFFS2)
which does wear leveling (writes are spread out over the
entire device, reducing the wear on any particular portion).
Also, move things that get updated a lot to a RAM disk and
only flush to the FLASH periodically.

BTW /proc is a pseudo file system - it is not represented
in any media like the FLASH.

> Thanks,
> Prakash
>
>
> Jaap Jan: Thank you very much for precise
> instructions.
>
>
>
>
> --- Jaap-Jan Boor <jjboor at lucent.com> wrote:
> > Prakash,
> >
> > You should divide your flash into parts. e.g.:
> >
> > - first block(s) boot
> > - then some blocks for the kernel
> > - all remaining blocks as root fs
> >
> > You do this partitioning in the maps directory of
> > drivers/mtd.
> >
> > You can make a linux kernel with mtd and jffs2
> > support and ramdisk that
> > holds the erase, eraseall, dd, mkfs.jffs2 etc.
> > programs.
> >
> > You can load the kernel into SDRAM, run it, prepare
> > your flash (erase flash, then use mkfs.jffs2 on a
> > /dev/mtd? device
> > to prepare an fs.
> >
> > You should then make a new kernel that uses mtd as
> > rootfs, not
> > the ramdisk as rootfs.
> >
> > Jaap-Jan
> >
> > Prakash kanthi wrote:
> > >
> > > Hi Jaap Jan,
> > >
> > > Thanks for your reply. What do you mean by 'works
> > out
> > > of the box with denx'? I see the code you referred
> > to
> > > but not sure how to use it. I still have some
> > > concerns. Like,
> > >
> > > 1. How can i initially store the image into flash?
> > My
> > > flash chip is on the board.
> > > 2. How can i boot linux from flash?
> > >
> > > 3. Currently i have a 32MB SDRAM along with flash.
> > I
> > > have tools to download linux image into SDRAM.
> > Even if
> > > i go with MTD/JFFS, my concern is unless linux
> > runs
> > > flash can not be accessed and vice versa.
> > >
> > > 4. Lets say, i download linux into a safe place in
> > > SDRAM, boot it and then access flash thru MTD/JFFS
> > and
> > > store linux image into flash. Even in this case,
> > what
> > > all i need to take care of for making my flash a
> > boot
> > > device.
> > >
> > > Any detailed documentation is appreciated.
> > >
> > > Thanks,
> > > Prakash
> > >
> > > --- Jaap-Jan Boor <jjboor at lucent.com> wrote:
> > > > Hi,
> > > >
> > > > I use strata flash with MTD and JFSS2 as file
> > system
> > > > on top of it. Works out of the box with denx'
> > eldk
> > > > kernel and
> > > > toolchain. I've provided my own flash map but
> > you
> > > > can also use an existing one (look e.g. in
> > > > linux/drivers/mtd/maps)
> > > >
> > > > Jaap-Jan
> > > >
> > > > Wolfgang Denk wrote:
> > > > >
> > > > > In message
> > > >
> > <20030326070131.88176.qmail at web41202.mail.yahoo.com>
> > > > you wrote:
> > > > > >
> > > > > > I have a 32MB Intel Strata flash on my
> > PPC405
> > > > based
> > > > > > custom board. I need to create access
> > > > routines/APIs to
> > > > > > access the flash. I was thinking of creating
> > a
> > > > Flash
> > > > > > File System and mount it as a device in
> > Linux
> > > > > > environment.
> > > > > >
> > > > > > Are there any off the shelf FFS packages
> > > > available?
> > > > > > Generally, how the flash is used?
> > > > >
> > > > > Use the MTD layer.
> > > > >
> > > > > > I am working with micro-monitor to use its
> > Tiny
> > > > File
> > > > > > System on flash support and eventually mount
> > > > into
> > > > > > linux. Did anyone use this combination
> > before?
> > > > >
> > > > > I think you cannot do this. AFAIK the TFS code
> > is
> > > > not available under
> > > > > a GPL compatible license which prevents it
> > from
> > > > being linked with the
> > > > > Linux kernel code.
> > > > >
> > > > > Best regards,
> > > > >
> > > > > Wolfgang Denk
> > > > >
> > > > > --
> > > > > Software Engineering:  Embedded and Realtime
> > > > Systems,  Embedded Linux
> > > > > Phone: (+49)-8142-4596-87  Fax:
> > (+49)-8142-4596-88
> > > >  Email: wd at denx.de
> > > > > There is is no reason for any individual to
> > have a
> > > > computer in  their
> > > > > home.      -- Ken Olsen (President of Digital
> > > > Equipment Corporation),
> > > > >               Convention of the World Future
> > > > Society, in Boston, 1977
> > > > >
> > > >
> > > > --
> > > > J.G.J. Boor
> > > > Room:  BE-525
> > > > Lucent Technologies Nederland b.v.
> > > > Phone: +31 35 687 4721
> > > > Optical Networking Group TMS Data
> > > > Fax:   +31 35 687 5976
> > > > P.O. Box 1168, 1200 BD, Hilversum, The
> > Netherlands
> > > mailto:jjboor at lucent.com
> > >
> >
> > --
> > J.G.J. Boor
> > Room:  BE-525
> > Lucent Technologies Nederland b.v.
> > Phone: +31 35 687 4721
> > Optical Networking Group TMS Data
> > Fax:   +31 35 687 5976
> > P.O. Box 1168, 1200 BD, Hilversum, The Netherlands
> mailto:jjboor at lucent.com
>
>

--
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|       Mind: Embedded Linux and eCos Development        |
|--------------------------------------------------------|
| Gary Thomas              email:  gary.thomas at mind.be   |
| Mind ( http://mind.be )  tel:    +1 (970) 229-1963     |
| gpg: http://www.chez-thomas.org/gary/gpg_key.asc       |
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