> Hi there,
>
> This is not exactly an specific ARM platform question, but I
> believe is of interest to the community,
> and I use an ARM platform anyway (ebsa285) where these ideas
> are put into practice.
>
> My question: what would be the best file system for an
> embedded platform that uses most of the fs as
> read-only, but needs write access for a few of state files?
> right now, the application runs on
> boot-up from an IDE, but if the users shut the box the "hard
> way", i.e., turn power off, fs gets
> messed up, as expected. It mostly comes back on the next
> boot-up after fsck, but it has also happened
> that the odd hard drive has died on us. It's not the way to go anyway.
> We've played with JFFS, but the memory overheads for the
> database are massive. I am aware of Cramfs, but
> not familiar with it. We've been playing also with ramdisks,
> and it works, but if it not unmounted on shutdown,
> the state information that needs to be saved up, is obviously lost.
>
> Has anybody out there faced a similar situation? any thoughts
> welcome. I am happy to keep trying all the
> available options.
>
> TIA
>
> Jaime
I think you'll find that a mix of filesystems may serve you better. The new
JFFS2 (JFFS with compression) seems to do almost as good of a job on
compression as cramfs so we've recently converted to using it in favor of
cramfs. Cramfs would be slightly more suitable for a read-only filesystem
that needs to stay read-only, but for most jobs jffs2 is easier to work
with. You would also get better load levelling over time with an all-jffs2
filesystem if you need to make occasional writes to flash.
Temporary files and things that change frequently at runtime (the /var and
/dev directory trees for example) we normally load into ramfs, which
dynamically sizes according to need, to save wear & tear on the flash.
Things which occasionally need changing (config files in /etc for example)
are left in flash. With jffs2 compression they take up even less space than
before. If you have a large database to maintain, if it can be made
read-only, cramfs should give you a somewhat smaller image than jffs2, but
probably not enough to make a difference unless you are *really* tight on
memory.
//Jeff
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