On Tue, Jan 20, 2004 at 04:53:15PM +0100, Urs Nietlispach wrote: > I'm on this list since a few weeks - but actually I'm not really sure if I'm > right here. > What I'm looking for is not so much 'embedded' in terms of very little space > like 8MB (the 1 lb bag..), > what I'm looking for is a linux which can be run stable for years on a CF > card. The main goal is stability, but there should also be SSL and the > standard network featurs. A GUI is not needed. > > Can anybody tell me where I can gather information about this? > What are the main approaches to keep the CF card alive?
A lot of applications do not need write access, or if they do(logs,..), writing to a RAM based fs(tmpfs,ramfs) works for things not requiring permanent storage. So easiest solution is to run on a read-only partition. If you wish to make changes, remount as rw, make changes, then go back to ro. Or use a few partitions, the main one ro, and a data partition mounted rw. You can compress about 2 to 1 with cramfs, but it's read only. jffs2 is designed for flash, and offers both write and compression, but I don't know if it makes sense to use it on CF. The longevity/reliability of flash for write operations is an interesting area to research. The vendors don't tell you a whole lot, or if they do it is not very specific. SanDisk has got some whitesheets on their site about wear leveling built in. http://www.openbrick.org project has a wiki with some good notes on CF. Sandisk is selling a Industrial grade that is rated at 2M read/writes instead of 300K. I was very interested in the wear leveling built in. From what SanDisk white paper tells, their controller wear-levels over smaller block areas, not the entire flash disk area. They suggest that some filesystems will move a file around enough on re-write to spread out the wear. I would like to find time to study file-system behavior to track where exactly on the disk it is writing files too. Anyone know how to determine what is the physical placement on disk of a certain file? I was looking for some inexpensive IDE to CF converters on ebay, ended up buying some IDE with CF modules attached: http://www.linnix.com I'm guessing that it's something thrown together by a hobbyist, but the price is right, and you have to like the domain name :) Haven't got em yet, so I can't comment further. So that has me wondering if the cheap USB flash stick I bought does wear leveling...
