Re: netapp-alike snapshots?

[Marc MERLIN <marc@merlins.org>]

On Sat, Sep 09, 2017 at 10:43:16PM +0300, Andrei Borzenkov wrote:
> 09.09.2017 16:44, Ulli Horlacher пишет:
> > 
> > Your tool does not create .snapshot subdirectories in EVERY directory like
> 
> Neither does NetApp. Those "directories" are magic handles that do not
> really exist.
 
Correct, thanks for saving me typing the same thing (I actually did work
at netapp many years back, so I'm familiar with how they work)

> > Netapp does.
> > Example:
> > 
> > framstag@fex:~: cd ~/Mail/.snapshot/
> > framstag@fex:~/Mail/.snapshot: l
> > lR-X - 2017-09-09 09:55 2017-09-09_0000.daily -> /local/home/.snapshot/2017-09-09_0000.daily/framstag/Mail
> 
> Apart from obvious problem with recursive directory traversal (NetApp
> .snapshot are not visible with normal directory list) those will also be
> captured in snapshots and cannot be removed. NetApp snapshots themselves
> do not expose .snapshot "directories".

Correct. Netapp knows this of course, which is why those .snapshot
directories are "magic" and hidden to ls(1), find(1) and others when
they do a readdir(3)

> > lR-X - 2017-09-09 14:00 2017-09-09_1400.hourly -> /local/home/.snapshot/2017-09-09_1400.hourly/framstag/Mail
> > lR-X - 2017-09-09 15:00 2017-09-09_1500.hourly -> /local/home/.snapshot/2017-09-09_1500.hourly/framstag/Mail
> > lR-X - 2017-09-09 15:18 2017-09-09_1518.single -> /local/home/.snapshot/2017-09-09_1518.single/framstag/Mail
> > lR-X - 2017-09-09 15:20 2017-09-09_1520.single -> /local/home/.snapshot/2017-09-09_1520.single/framstag/Mail
> > lR-X - 2017-09-09 15:22 2017-09-09_1522.single -> /local/home/.snapshot/2017-09-09_1522.single/framstag/Mail
> > 
> > My users (and I) need snapshots in this way.

You are used to them being there, I was too :)
While you could create lots of symlinks, I opted not to since it would
have littered the filesystem.
I can simply cd $(SNAPROOT)/volname_hourly/$(PWD)
and end up where I wanted to be.

I suppose you could make a snapcd shell function that does this for you.
The only issue is that volname_hourly comes before the rest of the path,
so you aren't given a list of all the snapshots available for a given
path, you have to cd into the given snapshot first, and then add the
path.
I agree it's not as nice as netapp, but honestly I don't think you can
do better with btrfs at this point.

Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/                         | PGP 1024R/763BE901