[zfs-discuss] [RFC] Improved versioned pointer algorithms

Akhilesh Mritunjai
Mon, 21 Jul 2008 04:38:20 -0000

> On Monday 14 July 2008 08:29, Akhilesh Mritunjai
> wrote:
> > Writable snapshots are called "clones" in zfs. So
> infact, you have
> > trees of snapshots and clones. Snapshots are
> read-only, and you can
> > create any number of "writable" clones from a
> snapshot, that behave
> > like a normal filesystem and you can again take
> snapshots of the
> > clones.
>
> So if I snapshot a filesystem, then clone it, then
> delete a file
> from both the clone and the original filesystem, the
> presence
> of the snapshot will prevent the file blocks from
> being recovered,
> and there is no way I can get rid of those blocks
> short of deleting
> both the clone and the snapshot.  Did I get that
> right?

Right. Snapshots are immutable. Isn''t this the whole point of a
snapshot ?

FS1(file1) -> Snapshot1 (file1)

delete FS1->file1 : Snapshot1->File1 is still intact

Snapshot1(file1) -> CloneFs1(file1)

delete CloneFS1->file1 : Snapshot1->File1 is still intact (snapshot is
immutable)

There is lot of information in zfs docs on zfs community. For low level info,
you may refer to ZFS on disc format document.

Regards
- Akhilesh


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