I read with interest your article (http://www.linuxdevices.com/articles/AT4540125636.html) on how you crammed Debian into a 32 mb compact flash on an openbrick E, as I did the same thing, but with a very different technique on my openbrick.
My openbrick serves as a wireless gateway, doing ppp dialup, but I also wanted it to be maximally flexible, so I could install new debian packages on demand, or use it for long overnight downloads, or reconfigure it temporarily as a desktop system, etc. I also wanted to be able to do the usual apt-get dance for security updates. At the same time, it will spend most of its time in a fairly demanding environment (high dust, +-40 degrees C temperature variations, often below-freezing temperatures). I concluded that I needed a hard drive in the machine for extra storage, but that it needed to default to not spinning, and be spun up only on explicit command. Since I wanted to be able to upgrade it on the fly, using a read-only compressed filesystem was out. I thought about JFFS2, but so far I have been able to get by without compressing the filesystem on the flash card. What I did was made the flash the root filesystem, and used a mixture of bind mounts, symlinks, and partial directory copies to move most of the innessential stuff to the hard disk. The hard disk is still used to boot (I haven't got a bootloader to work from the compact flash when the hard disk is also present), but is then unmounted and spun down. The compact flash root filesystem is mounted read-only with tmpfs for /tmp and most of /var. I think of this default state as "embedded mode"; the openbrick in this configuration is useful mostly as a wireless dialup gateway, dns server, dhcp server, etc. I can ssh in, but the environment is a bit limited. If I mount the hard drive though, it suddently becomes a full-fledged debian system. Remount the flash read/write and I can tweak the software, etc. I have been planning to package up the software I use to manage this split-personality system as a "flashhybrid" package. I need to add some more intelligence to make it easier to set up the initial system, and make it deal better with being upgraded on the fly. I think this approach may also be useful for things like ipaq's with piggy-back microdrives. OTOH with luck 64 or 128 mb flash cards, large enough for a full debian system with little or no hackery, might become common and cheap enough before I finish it to make it obsolete. :-) -- see shy jo
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