On Wed, Aug 5, 2009 at 10:46 PM, Christian Mikovits<gae...@luchmhor.net> wrote: > I guess whats really hard to program: snapshot removal when not > copying the data, but only pointing to that data and writing the > differences from that point on. Figure out how difficult it is to > remove snapshot 3 of 7; When snapshot 1 is the original data, snap2 > the diff from 1 to 2, snap 3 the diff from 2 to 3, .... so you have to > merge the data of snap 3 and 4.
Depends on the snapshot design: if snapshots are implemented with reference counts, nothing needs to be merged (but simplicity in this respect comes at the cost of garbage collection). Regards, Andrey > > But the benefits are obvious: instant snapshots and very low space > consumption (in case you don't delete lots of your 'live' data). > > On 8/5/09, Andrey Kuzmin <andrey.v.kuz...@gmail.com> wrote: >> On Wed, Aug 5, 2009 at 3:18 PM, Roy Sigurd Karlsbakk <r...@karlsbakk.net> >> wrote: >>> >>> On 4. aug.. 2009, at 20.33, Chris Mason wrote: >>> >>>>> It's strange that such a small thing should be delayed so much. If >>>>> snapshot removal was working, I'm quite sure we might get more users >>>>> and thereby more stable code faster. >>>> >>>> It's a small feature but it gets deep into the difficult parts of the >>>> dentry cache to do it right. So, it definitely isn't easy. >>> >>> >>> I'd say it's a pretty elemetary feature to be able to remove something you >>> have created. >> >> Snapshots are somewhat counter-intuitive in many respects: for >> instance, one snapshot-capable file-system performs writes to a >> dataset with snapshots _faster_ than to the same dataset w/o >> snapshots. Snapshot removal is no exception - it's a bit more complex >> than one would think. >> >> Regards, >> Andrey >> >>> I know, you can remove the files and so on, but still, having a bunch of >>> old and empty >>> snapshots lying around is no good. >> >> >>> >>> roy >>> -- >>> Roy Sigurd Karlsbakk >>> (+47) 97542685 >>> r...@karlsbakk.net >>> http://blogg.karlsbakk.net/ >>> -- >>> I all pedagogikk er det essensielt at pensum presenteres intelligibelt. >>> Det er et elementært imperativ for alle pedagoger å unngå eksessiv >>> anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfeller >>> eksisterer adekvate og relevante synonymer på norsk. >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >>> the body of a message to majord...@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majord...@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
