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 "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) 99.26% setiathome rank, not too shabby for a WV hillbilly Yahoo.com attorneys please note, additions to this message by Gene Heskett are: Copyright 2004 by Maurice Eugene Heskett, all rights reserved.
