[NCLUG] Backup idea

[Bob Proulx]

Sean Reifschneider wrote:
> Bob Proulx wrote:
> > Hmm...  This sounds very much like 'pdumpfs'.
>
> I'd guess it's an implementation of the fairly common recipe of doing an
> rsync and then "cp -al" of that directory to one named for the current
> date.  Pretty common...

You are right.  The idea is a good basic idea and so there will almost
certainly be many implementations of it.  Mostly it gave me a good
opportunity to advocate for pdumpfs since I think it is a nice one.

> The down side is that it takes quite a lot of time to remove the daily
> snapshots, and large files that change a bit regularly consume vast amounts
> of memory.  A 2GB log file that gets small additions every day will grow by
> another 2GB daily...

Yep.  But I find removing them goes fairly quickly.  Certainly faster
than the making of them in the first place.  Since this happens by
cron in the time I choose to be away I never really notice.  The main
place I use pdumpfs is on a Debian depot daily mirror.  Everything is
already compressed pretty well in that case.

And a general problem with "near"-line backups on a disk is that they
don't provide good serious disaster relief.  If the online backups
fail then it can be difficult to go back long before that.  Think of a
flood.  But a hard media backup such as on dvd would probably survive.

I try to make sure my online photo album has multiple dvd copies in
different locations.  That is the one thing that I would really hate
to lose.

> In the past if your snapshot volume ran out of space, you were out
> of luck.

That is a little vague, "you were out of luck."  Does that mean that
the filesystem crashed or acted full or ... ??  Can you clarify your
meaning there?  I seem to recall that it used to crash and the
filesystem became corrupted but I hated to say that without a little
more memory of the problem.  I can't believe that it is still like
that now.  I think the logical thing for it to do would be to behave
like a full filesystem.

> Try using rdiffbackup.

I have heard of it.  I will add it to my list of things to look into.

> If, if you're up for an adventure, ZFS has great snapshot support.

Adventure in backups?  That is the one place where I usually want to
avoid excitement.  :-) :-)

Bob