Re: Transparent compression in the FS

[Davide Libenzi]

On Thu, 16 Oct 2003 jlnance@xxxxxxxxxxxxxx wrote:

> On Thu, Oct 16, 2003 at 04:04:48PM -0700, jw schultz wrote:
> >
> > The idea of this sort of block level hashing to allow
> > sharing of identical blocks seems attractive but i wouldn't
> > trust any design that did not accept as given that there
> > would be false positives.
>
> But at the same time we rely on TCP/IP which uses a hash (checksum)
> to detect back packets.  It seems to work well in practice even
> though the hash is weak and the network corrupts a lot of packets.
>
> Lots of machines dont have ECC ram and seem to work reasonably well.
>
> It seems like these two are a lot more likely to bit you than hash
> collisions in MD5.  But Ill have to go read the paper to see what
> Im missing.

The TCP/ECC thingies are different since the probability of false
negatives is the combined probability that 1) the data is wrong 2) the
hash collides. In case of a hash-indexing algo the probability of coliding
hashes is "raw".



- Davide

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