Messages in this thread |  | | Date | Fri, 27 Apr 2001 18:53:07 +0100 | From | Padraig Brady <> | Subject | Re: ramdisk/tmpfs/ramfs/memfs ? |
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David Woodhouse wrote: > > padraig@antefacto.com said: > > btw I get my initial root filesystem from a compact flash that can be > > accessed just like a hardisk. It's writeable also like a harddisk, but > > we boot with it readonly, and only mount it rw if we want to save > > config or whatever. We definitely wouldn't swap to it as it has > > limited erase/write cycles. The filesystem is compressed ext2. > > Why copy it into RAM? Why not use cramfs and either turn the writable > directories into symlinks into a ramfs which you create at boot time, or > union-mount a ramfs over the top of it?
? I never said I copied it into RAM. The ramfs is just used for /tmp & /var which are symlinks on the flash. I didn't know you could read/write cramfs like ext2/JFFS2? I still want to be able to update/create/delete files like a normal ext2 partition. Oh I see the confusion, sorry my fault, when I said the root filesystem is compressed ext2, I meant it's ext2 with chattr +c done on all files (the e2compr patch implmenents it). By the way why isn't e2compr a standard part of the kernel. I've have no problems at all with it.
I didn't know about union-mounting, seems useful.
As for whether to use tmpfs/ramfs I think they do basically the same thing only the implementation is different. tmpfs uses shared mem and so is probably more portable than ramfs which it tightly coupled with VFS. I think I'll use ramfs (with limits patch) so.
> padraig@antefacto.com said: > > As for using JFFS2 + MTD ramdisk intead of ext2+e2compr+ramdisk is not > > an option as the only advantage would be journalling, you still can't > > resize. IMHO JFFS is only required where you have flash without an IDE > > interface. > > True. We are currently lacking a compact, compressing, journalling > filesystem for use on block devices. It's been suggested that we could make > JFFS2 work on them, by making a fake MTD device which uses a block device > as backing store. Nobody's yet shown me the code though :)
How much more efficent is JFFS than say ext3+e3compr, wrt: logic size/logic speed/RAM requirements/filesystem structure size.
> -- > dwmw2
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