On 07/06/2012 01:55 PM, Chris Mason wrote: > On Fri, Jul 06, 2012 at 02:51:43AM -0600, Alexander Block wrote: >> On Fri, Jul 6, 2012 at 12:34 AM, Goffredo Baroncelli <[email protected]> >> wrote: >>> On 07/05/2012 06:51 PM, Alexander Block wrote: >>>> Hello all, >>>> >>>> in IRC we had a discussion on how we could solve sending live >>>> subvolumes and how to send subvolumes without the need to >>>> administrate/keep old snapshots for incremental sends. One of the >>>> ideas was to introduce "sendshots", which are basically snapshots >>>> where no refs are counted for file data. This means, that when file >>>> data is changed in the sendshot origin, we do not consume extra space >>>> for two copies of the data. We would only have the metadata >>>> duplicated. >>>> >>>> For the initial btrfs send we could do this: >>>> 1. Create a hidden read-only snapshot of the subvolume to send. Hidden >>>> means that it's not referenced by any subvolume. It is however still a >>>> normal snapshot (not a sendshot!). Hidden snapshots are not possible >>>> atm so we would have to implement that. This step allows us to send >>>> read-write subvolumes, because we have a freezed version of it. >>> >>> Why we should want/need an hidden snapshot ? We could put this kind of >>> hidden snapshot under a directory dot-prefixed (like /.hidden-subvolumes) >> That would have the problem that the user may modify the subvolume >> in-between (by removing the ro flag). Or he could simple cd into it >> and we would later fail to delete it. > > I prefer to make this more explicit. We could add a hard-readonly flag > that cannot be cleared. Having the snapshot show in the FS lets the > admin know what things are really using space.
Me too, but I am guessing what should happens when the users try to read an old data ? (I am talking about sendshot ). If I understood correctly the old data isn't tracked by the sendshot. GB -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
