Yes, I think for many applications, you can close files when they do not need to be open, and anticipate when power would/could be turned off. For one of my applications, if the train is not moving, I can close the files and buffer any events in memory. When the train IS moving, we should NOT lose power, and if we do, we have a lot bigger problems than losing a block of flash memory on the SD card. Heck in my application, I might even run directly off of the batteries, and power myself down when the train is shut off. Don.
On 6/22/06, Jesse Off <> wrote:
BSD uses a technique dubbed "soft-deps" on its filesystem which does
not require a journal. It acheives about the same benefits of a
meta-data journaled filesystem without the extra writes.
http://www.mckusick.com/softdep/
I have some history with another filesystem called LFS. (log-
structured filesystem) This FS is "pure-journaled" and not
just "metadata journaled" like (I presume) EXT3. Pure-journaled
filesystem designs (like YAFFS2) do not need extra block writes to
commit the journal and would represent about the closest thing to
perfection as far as general purpose flash filesystems go.
Unfortunately, you cannot use YAFFS2 with a traditional block device
like SD or a hard drive -- it needs flash, and more specifically,
commodity NAND flash chips in their raw interface.
If there are any generic Linux filesystem types that are "pure-
journaled", that would be IMHO preferred choice #1. #2 would be
something with metadata ordering such as softdep. #3 would be
hybrid meta-data journaled fs's like EXT3 or traditional filesystems
such as FAT/EXT2 mounted with sync & noatime.
Another thing you must consider if you're trying to accomodate
someone yanking power in the middle of operation is that if there
just happens to be a flash write going on when power collapses, you
will likely loose 1 block of flash permanently irrespective of FS.
I believe this is also the case with SD. You usually don't have
anything to worry about since SD will then remap a sector from its
spare pool and YAFFS2 will probably just never use that block again
(thereby decreasing free space).
//Jesse Off
--- In ts-7000%40yahoogroups.com, "Don W. Carr" <> wrote:
>
> This brings us back to using a journaling file system on SD flash
cards. I
> am thinking if you have a big enough flash that distributes the
writes, it
> should not be a problem. I really would like to know how many
extra writes
> there are with a journaling file system. Don.
>
> On 6/21/06, suptouch <> wrote:
> >
> >
> >
> > > We should release these modifications within a few days...
We're
> > > still trying to squeeze a few more tenths of a second. Below
is the
> > > output of the fastboot dump-- as you can see we don't print
kernel
> > > messages any more either (we got a couple tenths of a second
from
> > > that)
> > > //Jesse Off
> >
> > Good news ! so I'm waiting fo this modification with a new TS-
BOOTROM
> > and a new INITRD. Perhaps you can create two INITRD, one to
start the
> > Debian and the second to start the TS-linux (lighter than the
debian).
> >
> > About the linux root filesystem, which robust filesystem can I
use
> > instead of the ext2 (sync+noatime) on the sdcard (yaffs2, jffs2,
etc.) ?
> > The goal is to allow power switch-off the power without the
command
> > "shutdown -h now" ?
> >
> > And to finish, about the power consumption, Can I use the 2mA
STOP
> > Mode of the EP9302 under linux (cpu stop) ? If yes, have you got
a
> > idea of the method ?
> >
> >
> >
>
>
>
> --
> Dr. Don W. Carr
> J. G. Montenegro 2258
> Guadalajara, Mexico
> +52-333-630-0704
> +52-333-836-4500 ext 2930
>
-- Dr. Don W. Carr J. G. Montenegro 2258 Guadalajara, Mexico +52-333-630-0704 +52-333-836-4500 ext 2930
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