On Sat, Jan 16, 2016 at 9:10 AM, Duncan <1i5t5.duncan@xxxxxxx> wrote: > Al posted on Sat, 16 Jan 2016 12:27:16 +0000 as excerpted: > >> Is there any urgency for dedup? What's wrong with storing the hash on >> disk with the block and having a separate process dedup the written data >> over time; > > There's actually uses for both inline and out-of-line[1] aka delayed > dedup. Btrfs already has a number of independent products doing various > forms of out-of-line dedup, so what's missing and being developed now is > the inline dedup option, which being directly in the write processing, > must be handled by btrfs itself -- it can't be primarily done by third > parties with just a few kernel calls, like out-of-line dedup can. Does the out-of-line dedup option actually utilize stored hashes, or is it forced to re-read all the data to compute hashes? If it is collecting checksums/etc is this done efficiently? I think he is actually suggesting a hybrid approach where a bit of effort is done during operations to greatly streamline out-of-line deduplication. I'm not sure how close we are to that already, or if any room for improvement remains. -- Rich -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
