At Thu, 12 Feb 2015 15:49:00 +0800, Liu Yuan wrote: > > On Thu, Feb 12, 2015 at 04:40:56PM +0900, Hitoshi Mitake wrote: > > At Thu, 12 Feb 2015 15:31:15 +0800, > > Liu Yuan wrote: > > > > > > On Thu, Feb 12, 2015 at 03:59:51PM +0900, Hitoshi Mitake wrote: > > > > At Thu, 12 Feb 2015 14:38:37 +0800, > > > > Liu Yuan wrote: > > > > > > > > > > On Mon, Feb 09, 2015 at 05:25:48PM +0900, Hitoshi Mitake wrote: > > > > > > Current "dog vdi snapshot" command creates a new snapshot > > > > > > unconditionally, even if a working VDI doesn't have its own > > > > > > objects. In such a case, the created snapshot is redundant because > > > > > > same VDI is already existing. > > > > > > > > > > What kind of use case will create two identical snapshots? This logic > > > > > is simple > > > > > and code is clean, but I doubt if there is real users of this option. > > > > > > > > Generally speaking, taking snapshot periodically is an ordinal usecase > > > > of enterprise SAN. Of course sheepdog can support this use case. In a > > > > case of sheepdog, making cron job (e.g. daily) which invokes "dog vdi > > > > snapshot" simply enables it. > > > > > > > > But if a VDI doesn't have COWed objects, the snapshot will be > > > > redundant. So I want to add this option. > > > > > > Okay, your patch makes sense for periodic snapshot. But if dog have found > > > identical snapshots, it won't create a new one and return success to the > > > caller. > > > > > > I assume the caller is some middleware, if there is no new vdi returned, > > > will > > > this cause trouble for it? This means it will need to call 'vdi list' to > > > check > > > if new vdi created or not? > > > > So I'm adding this feature with the new option. Existing semantics > > isn't affected. And if checking process (has_own_objects()) faces > > error, it is reported correctly to middleware. > > > > > > > > I'm not agasint this patch, but I have some questions. For identical > > > snapshots, > > > the overhead is just an inode object created, no? Looks to me the > > > overhead is > > > quite small and no need a special option to remove it. > > > > Taking snapshots of thousands of VDIs will consume thousands of VID, > > and create thousands * replication factor of inodes. I'm not sure the > > consumption of VID will become serious problem, but inodes will make > > replication time longer (e.g. 16:4 ec requires 20 inodes). > > Yes, this is the point. Make sense to me. I have some comments to the code in > my last email. Could you submit a V2? BTW, it would be great if you can > include > above rationale into the commit log.
OK, I'll send v2 later. Thanks, Hitoshi > > Thanks > Yuan > -- > sheepdog mailing list > sheepdog@lists.wpkg.org > https://lists.wpkg.org/mailman/listinfo/sheepdog -- sheepdog mailing list sheepdog@lists.wpkg.org https://lists.wpkg.org/mailman/listinfo/sheepdog