On Wed, Dec 25, 2019 at 2:58 PM Till Wegmüller <toaster...@gmail.com> wrote:
> I can't remember where I learned it but I know what they mean. > > I think all if from the zfs man page. > > Refer is short for Blocks referenced. It shows the size of the > Filesystem table at that the Snapshot or Dataset References. Even if the > Blocks on disk are not related to that snapshot. "Not related" doesn't sound like the right way to phrase it, "not deleted since" would be somewhat better - however, zfs snapshots are not implemented as "diffs" from a previous state (unlike virtualbox disk snapshots, which have to operate oblivious to the filesystem being used). Every zfs snapshot is basically a reference to the root of a filesystem tree, which has full references to the entire filesystem as it was at the point the snapshot was taken. The sharing of unmodified data between snapshots is simply that many nodes in this tree are the same exact blocks on disk as they are in some other snapshot's tree (or the live filesystem tree). Thus, "referenced" is the full size of the filesystem as it was at the time of the snapshot. "Used", for the filesystem itself, instead reports all blocks referenced by the filesystem, all its snapshots, and all child filesystems and their snapshots (without counting any block twice). If you want to know which snapshots are holding onto the most "old" blocks, you can either mess around with 'zfs destroy -nv', or you can use zfs properties like 'written@<snapshot>' to back-calculate how much has been deleted/overwritten between snapshots. I have a pair of scripts that use the second way, snapspace and snapreport, here: https://github.com/coalsont/zfs-scripts snapspace is the simpler and more useful one, snapreport is mainly meant for figuring out ambiguous situations. _______________________________________________ openindiana-discuss mailing list openindiana-discuss@openindiana.org https://openindiana.org/mailman/listinfo/openindiana-discuss
