Hmm, if it were collision resistant, wouldn't that mean that you would need one server for each file you want to store? I suspect you want many collisions, just a good even distribution of those collisions, -Martin --- On Tue, 1/5/10, Jeff Darcy <jdarcy@xxxxxxxxxx> wrote: > From: Jeff Darcy <jdarcy@xxxxxxxxxx> > Subject: Faster hashing for DHT > To: gluster-devel@xxxxxxxxxx > Date: Tuesday, January 5, 2010, 12:12 PM > While looking at the DHT code, I > noticed that it's using a 10-round > Davies-Meyer construction to generate the hashes used for > file > placement. A little surprised, by this, I ran it by a > couple of friends > who are experts in both cryptography and distributed data > storage. The > consensus seems to be that the hash used for this purpose > needs to be > collision resistant but not cryptographically strong. > One theorized > that the choice made in DHT is probably based on prior > examples (e.g. > Freenet and Mojo Nation) where cryptographically strong > hashes were > chosen, but that the requirements driving those decisions > probably don't > apply to GlusterFS. This is a non-trivial issue > because these hashes > are used quite frequently and the current one is quite > computationally > expensive. I note that Hsieh's SuperFastHash is > already implemented in > GlusterFS and is used for other purposes. It's about > 3x as fast as the > DM hash, and has better collision resistance as well. > MurmurHash > (http://murmurhash.googlepages.com/) is even faster and > more collision > resistant. For future releases, I suggest dropping > the DM hash and > switching to one of these others. > > > _______________________________________________ > Gluster-devel mailing list > Gluster-devel@xxxxxxxxxx > http://lists.nongnu.org/mailman/listinfo/gluster-devel >
