Linux Compact Flash Write Filter akin to XPe EWF
Chris Morley
Filter, which basically will write all system changes to a ram disk
which can, if required, be committed to disk by the user via a write
utility. If power is removed and changes not committed to disk all
changes will be lost.
The reason i am after this is because i wish to run Linux on compact
flash. I have been messing around with pfsense firewall but it
transpires i need something a bit more flexible, a Linux based install
which can run on compact flash with minimal disk writes to compact
flash to ensure the CF card doesn't die, but also with the ability to
update the file system and install custom packages, install from
source etc.
It would be ideal to have BSD (ok not linux but dont want to get OT
here), CentOS or similair running on CF card, i know people talk about
make the file system Read Only but then that has issues with certain
packages in the system that need write access, would be nice if these
changes could be committed one as off writes.
Have searched for a compact flash enabled distribution but with the
benefits and flexibility of installing packages via apt-get etc but
cannot find one, hence my idea that a write filter driver which could
sit in between the CF card and IDE driver would be great... then i
would get the benefit of both worlds.
Any ideas? Any recommendations to a an existing CF based linux distro
would be great, but as this is for a number of router boxes that need
to be up and running in a short space of time i dont want to spend too
much time on the development side of it. Plug and play write filter
driver would be best.
Many thanks in advance,
Chris
David Brown
If you are looking for firewall/router type distributions, there are a
number of Linux-based distros (openwrt, SmoothWall, IPCop, etc.).
I don't expect you will find anything like the EWF you describe for
Linux - you don't need it. XPe would need something like that because
it writes all sorts of junk to different places in the file system
(especially the registry) even while it's doing nothing of interest.
With Linux, there is a much clearer modularisation in the file system,
so it is easy to put parts in a ram disk (especially tmpfs) if you don't
want to write to a flash disk. If you put /tmp, /var/log, and /var/lock
on tmpfs, there is little that will be written to the disk except what
you want to write.
Chris Morley
wrote:
>
> - Show quoted text -
Thanks for the reply, i have been through them all... i use OpenWRT on
WRT 54G hardware and its excellent. However its not supported on x86
as thats beta. I have used Smoothwall, IPCop, M0n0Wall and eventually
used pfsense which is the most flexible however it seems to have
issues with site to site OpenVPN and isnt as flexible as i would like.
I could chuck on a full version of Linux on a real harddisk however i
would be concerned of reliability issues if the drive died as this is
for a rotuer. To this end, i have found Voyage Linux, an embedded
Debian install which has support for apt and committable file system
thus preserving the file system life. Looks good will check it out.
Hopefully i can have the best of both worlds!
Regards,
Chris
David Brown
<snip>
> Thanks for the reply, i have been through them all... i use OpenWRT on
> WRT 54G hardware and its excellent. However its not supported on x86
> as thats beta. I have used Smoothwall, IPCop, M0n0Wall and eventually
> used pfsense which is the most flexible however it seems to have
> issues with site to site OpenVPN and isnt as flexible as i would like.
>
> I could chuck on a full version of Linux on a real harddisk however i
> would be concerned of reliability issues if the drive died as this is
> for a rotuer. To this end, i have found Voyage Linux, an embedded
> Debian install which has support for apt and committable file system
> thus preserving the file system life. Looks good will check it out.
> Hopefully i can have the best of both worlds!
>
I haven't tried Voyage Linux myself, although I've read a little about it.
If you want to avoid hard disk wear for long-term reliability (although
personally I have very seldom seen hard disk failures, even on machines
with a decade of hard service), you might consider using one of the
newer generation of flash disks with standard hard disk interfaces.
They cost a lot more per GB than normal hard disks, but you don't need a
large one for a router. Their MTBF is much higher than for rotating
disks, and you won't meet wear issues unless you specifically
continuously write huge amounts of data to them.
Other alternatives include using a distribution with no read-write media
at all. There are distros aimed at loading all the required software
from a CD or even a floppy, the loading their configuration from USB or
floppy, and keeping everything in memory rather than on disk. Obviously
that's a bit more awkward for configuration changes, and you need to
store your logs on an external machine, but they are great from a
security viewpoint - if the machine ever gets compromised, a reboot will
guaranteed restore the setup.
For the ultimate in low disk usage (and security), I remember reading an
article about running a Linux router in halt mode. Even when halted,
the kernel still passed network packets through the filter and routing
tables, but no file systems are mounted, and no processes can run (this
was on an earlier version of Linux - perhaps 2.0 or 2.2, and may not
work on more modern kernels).
mvh.,
David