Messages in this thread | | | Subject | Re: Idea about a disc backed ram filesystem | Date | Thu, 08 Jun 2006 17:51:28 -0400 | From | Horst von Brand <> |
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Sascha Nitsch <Sash_lkl@linuxhowtos.org> wrote: > this is (as of this writing) just an idea. > > === current state === > Currently we have ram filesystems (like tmpfs) and disc based file systems > (ext2/3, xfs, <insert your fav. fs>).
Right.
> tmpfs is extremely fast but suffers from data losses from restarts, crashes > and power outages.
Part of the design tradeoffs.
> Disc access is slow against a ram based fs.
On-disk filesystems (and block device handling) are designed around that fact.
> === the idea === > My idea is to mix them to the following hybrid: > - mount the new fs over an existing dir as an overlay > - all files overlayed are still accessible > - after the first read, the file stays in memory (like a file cache) > - all writes are flushed out to the underlying fs (maybe done async) > - all reads are always done from the memory cache unless they are not cached > yet > - the cache stays until the partition is unmounted > - the maximum size of the overlayed filesystem could be physical ram/2 (like tmpfs)
But the current on.disk filesystems use caching of data in RAM extensively, /without/ having to keep the whole file in memory, just the pieces currently in active use. Your proposal negates the RAM for caches, so it would be much /slower/ than the current on-disk filesystems.
BTW, many of the live-CD distributions do exactly this (RAM overlay over a CD-based filesystem). -- Dr. Horst H. von Brand User #22616 counter.li.org Departamento de Informatica Fono: +56 32 654431 Universidad Tecnica Federico Santa Maria +56 32 654239 Casilla 110-V, Valparaiso, Chile Fax: +56 32 797513 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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