On Wed, Nov 26, 2014 at 07:07:22PM -0500, Mike Snitzer wrote: > On Wed, Nov 26 2014 at 6:47pm -0500, > Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > > > Sigh... > > > > Well, I wrote up a preliminary version of dm-checksum and then > > realized that I've pretty much just built a crappier version of > > dm-dedupe, but without the dedupe part. Given that it stores > > checksums in a btree which claims to be robust through failures and > > gives us automatic deduplication, I wonder if it we could achieve our > > aims by modifying dm-dedupe to verify the checksums on the read path? > > > > I guess it would be interesting to see how bad the performance hit is > > with the online dedupe part enabled or disabled. dm-dedupe v2 went > > out on the mailing list last August, which I missed. :( > > > > Unless... there's a specific reason nobody mentioned dm-dedupe here? > > As you may have seen in the dm-dedup thread, we need to actively > review/test that target It was in fact today's exchange on that thread that made me slap myself on the forehead and utter "D'oh!". > (if your initial review focus is on extending it > to _optionally_ verify the checksums on the read path then so be it). Yes, sorry, I meant to say "optionally to verify" in there. Adding a minor feature like that might be a good check to make sure I actually understand what's going on. :) > See: https://www.redhat.com/archives/dm-devel/2014-November/msg00114.html > Specifically, the git branch that builds on v2 based on my initial > review of v2: > > git://git.fsl.cs.stonybrook.edu/scm/git/linux-dmdedup > branch: dm-dedup-devel > > Your help on getting dm-dedup upstream would be very much appreciated. <-- reading the OLS paper, as a start. What happens to the metadata btree if someone sets the chunk size to 4KB? Will it become ungainly huge? The thing that I wrote simply wrote a block's worth of checksums inline with the data, which required a certain amount of slicing and dicing of bios but wasn't too horrible with performance. --D > > Thanks, > Mike > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
