At Mon, 14 Oct 2013 11:52:50 -0500 "John G. Heim" <jh...@math.wisc.edu> wrote:
> > > > > > > How 'full' are the tapes you have been using, on average? How many tapes > > has > > Amanda been using daily, on average? Peak? Just because your physical > > tapes > > have an arbitriarly large capacity (and the compressed capacity is very data > > dependent and is meaningless if Amanda is writing compressed dumps to the > > tape) does not mean that Amanda is actually using the whole tape (or even > > needs to). > > The changer broke so long ago I'm not sure. IIRC, most days it was > around 50%. But we were doing backups just twice a week, Mondays and > Thursdays. We sent the thing out to be repaired twice and it always > worked for a week or two and then broke again. It's out of warranty now > so it's done. > > > > > If your *average* daily dump is 20Gb, then your tape size should be about > > 20Gb > > (or maybe a little larger), and you will use 1 'tape' a day (on average). > > When > > Amanda does a 'full', you will need more 'tapes' (eg your peak usage -- set > > numtapes to allow for that). > > But if the full backup is 1.2Tb, wouldn't I'd have to set runtapes at 60 > if the capacity of each tape was 20Gb? I guess this is another question > (although somewhat related). If I have 1.2Tb to backup to start with, > how is amanda going to deal with that with a set of fresh, new virtual > tapes? It depends. Are you compressing the backups? Even though the raw data is 1.2Tb, it is likely to be smaller once compressed, depending on how well it compresses. Is this 1.2Tb on one file system or on several? If several, then Amanda can stagger the fulls over several days. This is one of the downsides of creating monolithic huge file systems (other than issues like it taking hours to do fsck's). > > I already tried it with the 80Gb virtual tapes. I had runtapes set to 3 > so I had to run amflush a bunch of times to finish the backup. But when > it was done I had 1.2Tb on the backup disk just as I expected. At the > time, I thought I knew what I was doing. But now I'm not so sure because > now I an out of tapes. > > > > You have to understand: Amanda will only put one day's worth of backups on a > > given tape. When amdump starts, it will *always* use fresh tapes. There is > > little point in making the tapes larger than the size of one day's backup. > > With your daily incrementals being about 20Gb, a tape size much larger than > > 20Gb is useless. You might be better off with *smaller* tapes and more of > > them. > > Right now, I don't know what the largest daily incremental backup would > be. I'm guessing that if the average is 20Gb, it probably goes as high > as 40Gb occasionally. So I figred 2x the average incremental backup size > was the minimum and 4x was safer. Hence the 80Gb. (20Gb x 4 = 80Gb) > > What is the downside to defining huge virtual tapes? I've already > created 25 80Gb tapes. That's 2Tb but it looks like if you write only > 20Gb to a tape, it takes up only 20Gb on disk. So I figured there was no > downside to creating huge virtual tapes. There isn't really a downside to defining huge virtual tapes, per sa. > > It occurs to me that perhaps my real problem is that I don't know how to > deal with the fact that my full backup is 1.2Tb whereas an incremental > backup is only 20Gb. That's a ratio of 60 to 1. But that can't be that > freakish. > > > Maybe I should create 80 25Gb tapes, set runtapes -- well, how about > just setting it to 80 for the first backup. Then set it back to 2 (just > in case) after that. That might make sense. There isn't any harm in leaving it at 80. You might also want to make sure amanda is set to aggressive bump -- you proabably don't really want amanda to make multiple full backups (which she will do by default). BTW: You should always do a 'Reply All' to include the whole list. Just in case I don't know what I am talking about (I am hardly an expert with Amanda, just somewhat experienced in using it with virtual tapes -- the only kind I have dealth with). I re-added the list address to the Cc list. > > -- Robert Heller -- 978-544-6933 / hel...@deepsoft.com Deepwoods Software -- http://www.deepsoft.com/ () ascii ribbon campaign -- against html e-mail /\ www.asciiribbon.org -- against proprietary attachments
