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    SubjectRe: ramdisk/tmpfs/ramfs/memfs ?
    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

    Padraig.
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