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SubjectRe: [RFC] mount flag "direct" (fwd)
On Wed, 4 Sep 2002, Daniel Phillips wrote:

> You're well wide of the mark here, in that you're relying on the assumption
> that caching is important to the application he has in mind. The raw transfer
> bandwidth may well be sufficient, especially if it is unimpeded by being
> funneled through a bottleneck like our vfs cache.

the fact that he is saying that this needs to run normal filesystems tells
us that.

if you need a filesystem to max out transfer rate and don't want to have
it cache things that is a VERY specialized thing and not something that
will match what NTFS/XFS/JFS/ReiserFS/ext2 etc are going to be used for.

either he has a very specialized need (in which case a specialized
filesystem is probably the best bet anyway) or he is trying to support
normal uses (in which case caching is important)

however the point is that the read-modify-write cycle is a form of cache,
it is only safe if you aquire a lock at the beginning of it and release it
at the end. A standard filesystem won't do this, this is what makes a DFS.

David Lang

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