Re: ext2 in a dos file/partition

Werner Almesberger (almesber@lrc.epfl.ch)
Thu, 7 Mar 1996 15:40:15 +0100 (MET)

> A big disadvantage is that umsdos is supposedly very slow.
[...]
> When I worked on vax/vms years ago, we had a similar thing, it was called a
> "virtual disk"; the file in which it lived was called a "container file".
> (It's very similar to the CVS of drvspace and stacker). You could mount the
> virtual disk, format it, etc. just as if it was a real disk.

While the loopback devices will let you do that, I have some doubts that
it will help performance in the general case, because you now depend
on the FAT cache in addition to the buffer cache. Not a good idea.

Note that you can increase the FAT cache a bit, but you shouldn't make
it too large, because the access time for all operations (lookup, add,
and invalidate) is O(n). I don't know how much "too large" is, but it
it would be really nice if somebody could run benchmarks to find the
break-even point on a slow PC.

- Werner

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