On Friday 24 September 2004 09:53, Ivan Petrovich wrote:
>Gene,
>
>> I'm puzzled, 4 days, but 5 tapes?  Whats the 5th tape?
>
>I thought that's what you're supposed to do: (tapecycle >=
>runspercycle + 1). This will keep the 5th run from writing over the
>first tape.
>
>> 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.
>
>What this means is: unless I preserve tapes from the previous cycle,
>tapes for one cycle can only guarantee that a file can be restored
> to its state _sometime_ in that cycle.
>
>The more traditional full/incremental backup scheme allows you to,
>in the case of a 7-day cycle, have the confidence that you can
> restore a file to its state on any of the last 7 days. But that
> isn't true with Amanda. :(
>
>Regards,
>
>Ivan

I don't believe thats true of any of the other backup thingies I've 
delt with Ivan, which includes bru, arkeia and diavolo pro.  And this 
is the reason I said that you will need the last runspercyle*runtapes 
tapes on hand for any full restore.  In my case, I've not yet (just 
getting restarted here) performed enough backups to have that many 
'tapes' on hand, but I will in another day or 3.

Keeping 2 full runspercycle*runtapes on hand is prudent, more could be 
called paranoid by some wags here, so I guess I am, just a wee tiny 
bit :)

-- 
Cheers, Gene
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Copyright 2004 by Maurice Eugene Heskett, all rights reserved.