From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrey Kuzmin Subject: Re: snapshot-removal - timeline ? Date: Wed, 5 Aug 2009 23:40:14 +0400 Message-ID: <2a31deca0908051240n7bbe0766i22f1330a86eef29f@mail.gmail.com> References: <1552F85577A149D68B0BFF2A44E0FF0A@bui.materna.com> <20090803130412.GB3570@think> <10F3F7E4-276B-49C3-B944-61320D634C93@karlsbakk.net> <20090803161800.GB5492@think> <7EC11C2E-889E-42A4-80D8-EA7E80F4963D@karlsbakk.net> <20090804183307.GG5693@think> <5D3C1A84-7A56-48CC-9C78-EDC582ED6B54@karlsbakk.net> <2a31deca0908051128r48cdfd62t2d0fe40c4a9b1a05@mail.gmail.com> <87c1d2600908051146n31f485f6qe51eb8509461ee75@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: linux-btrfs To: Christian Mikovits Return-path: In-Reply-To: <87c1d2600908051146n31f485f6qe51eb8509461ee75@mail.gmail.com> List-ID: On Wed, Aug 5, 2009 at 10:46 PM, Christian Mikovits 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 t= o > 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 wrote: >> On Wed, Aug 5, 2009 at 3:18 PM, Roy Sigurd Karlsbakk >> wrote: >>> >>> On 4. aug.. 2009, at 20.33, Chris Mason wrote: >>> >>>>> It's strange that such a small thing should be delayed so much. I= f >>>>> snapshot removal was working, I'm quite sure we might get more us= ers >>>>> 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. =A0So, it definitely isn't easy. >>> >>> >>> I'd say it's a pretty elemetary feature to be able to remove someth= ing you >>> have created. >> >> Snapshots are somewhat counter-intuitive in many respects: for >> instance, one snapshot-capable file-system performs writes to =A0a >> dataset with snapshots _faster_ than to the same dataset w/o >> snapshots. Snapshot removal is no exception - it's a bit more comple= x >> than one would think. >> >> Regards, >> Andrey >> >>> I know, you can remove the files and so on, but still, having a bun= ch of >>> old and empty >>> snapshots lying around is no good. >> >> >>> >>> roy >>> -- >>> Roy Sigurd Karlsbakk >>> (+47) 97542685 >>> roy@karlsbakk.net >>> http://blogg.karlsbakk.net/ >>> -- >>> I all pedagogikk er det essensielt at pensum presenteres intelligib= elt. >>> Det er et element=E6rt imperativ for alle pedagoger =E5 unng=E5 eks= essiv >>> anvendelse av idiomer med fremmed opprinnelse. I de fleste tilfelle= r >>> eksisterer adekvate og relevante synonymer p=E5 norsk. >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-btr= fs" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at =A0http://vger.kernel.org/majordomo-info.htm= l >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrf= s" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at =A0http://vger.kernel.org/majordomo-info.html >> > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html