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Linux Compact Flash Write Filter akin to XPe EWF

Hi, i'm looking for a Linux equivalent of Windows XPe Enhanced Write 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

Reply to
Chris Morley
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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.

Reply to
David Brown

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

Reply to
Chris Morley

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

Reply to
David Brown

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