On Fri, 24 Sep 2004, Ivan Petrovich wrote:
> > Bear in mind that a full backup isn't any one tape, but every tape for 
> > the most recent dumpcycle days will be required to do a full bare 
> > metal recovery.
> 
> True. I didn't think of that. But this point to what I believe is a
> weakness of Amanda:
> 
> Say I have a 1 week dumpcycle, runspercycle = 7. And for simplicity,
> say I have 7 files: file_0 .. file_6. Also assume that every file is
> changed everyday so that a level 1 is needed everyday.
> 
> Also assume that we only do levels 0 and 1.
> 
> On Sunday, Amanda does a level 0 for file_0, and level 1 for all other
> files; on Monday, Amanda does a level 0 for file_1, and level 1 for
> all other files, and so on.
> 
> At the end of the week, I will have tapes from Sunday through
> Saturday. Let's call them "tape zero" .. "tape six."
> 
> Then my customer calls and asks me to restore a file as it was on
> Wednesday. I can do that easily for file_0, since the level 0 for that
> file is on "tape zero," backed up on Sunday; and I also have all the
> necessary level 1's for it. So I grab tape zero (Sunday's level 0) and
> tape three (Wednesday's level 1), run amrecover, and voila.
> 
> But if I were to need to recover file_5 "as it was on Wednesday," I
> would be out of luck. This is because among these 7 tapes, the only
> level 0 for file_5 is on tape five, backed up on Friday. All level 1's
> from tape zero through tape 4 for file_5 are useless unless I happen
> to have preserved the level 0 from the previous cycle.

AFAIK, incrementals are not done on individual files, but on file systems.
If a file on a file system being dumped using level 1 is changed, the whole
file is backed up.

So you do not need the level 0 to recover the state of that file like it was on
the day the level 1 was made. But you do need the level 0 to restore the state
of another file that wasn't changed and thus wasn't included in the level 1
dump.

Hence there's no such weakness.

Gr{oetje,eeting}s,

                                                Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert AT linux-m68k 
DOT org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                                            -- Linus Torvalds