[CentOS] Filesystem that doesn't store duplicate data

Is there such a filesystem available? It seems like it wouldn't be too hard to implement... Basically do things on a block by block basis. Store md5 of a block in the table, and when writing a new block, check if the md5 already exists and then point the new block to the old block. Since md5 is not guaranteed unique, might need to do a diff between the 2 blocks and if the blocks are indeed different, handle it somehow.

When modifying an existing block that has multiple pointers, copy the block and modify the new block.

I know I'm oversimplifying things a lot, but something like this could work, no? Would be a great filesystem to store backups on, or things like vmware volumes...

Russ Sent from my Verizon Wireless BlackBerry