So, you have 10 million web pages, but you don't have 10 Gb of disk space to spare? I dunno how much you are costing your company, but I'd be surprised you can come up with a good enough Bloom filter in such a short time that it costs less to implement that, than it costs to buy an extra disk. (It's just going to be scratch space, doesn't need to backup, so the costs of the extra disk space aren't much more than just the disk).