Messages in this thread | | | Date | Fri, 8 Mar 1996 02:17:32 +0100 | From | Andries.Brouwer@cwi ... | Subject | Re: ext2 in a dos file/partition |
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Werner Almesberger writes:
:: When I worked on vax/vms years ago, we had a thing called a :: "virtual disk"; the file in which it lived was called a "container file". :: 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.
Well, it seems to me that the only thing you require from the FAT file system is the bmap() function. [One might even check that the container file is consecutive, and in that case skip bmap() entirely.]
: 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.
But it is easy to change this O(n) into O(log n) with a somewhat larger constant, at least for lookup and add.
Andries
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