On Tue, 23 Nov 2010 12:35:10 -0500 upengan78 <amanda-fo...@backupcentral.com> wrote:
> Firstly, thanks for the response! > > 1. You have 50 gig under backup/amanda control, but how much data > are you currently backing up per week ? > > Currently not doing any backups through Amanda. I am trying to > understand this whole theory of numbers involved in configuration. I > want to start backing up a 50G partition with a Full backup on Monday > and incrementals on each day till next week's Monday. So I think for > 7 days I will have to backup 50G + 200M x 6 days = 50.6G . Let's say > 55G a week. If you have a dump cycle of 7, and expect 50 G per, then you need 50 x 3 G, or 150 G, plus some spare. > > My original configuration is with little idea. > dumpcycle 7 > runspercycle 7 > tapecycle 20 > I though above would yield me 7 Days of backup including 1 Full and 6 > incrementals in 1 dumpcycle and all 20 tapes will be used. I don't > know if I am right. You need 3 x dump cycle tapes plus some spares, so I'd bump that up to 25, a nice integer factor of 150. The reason you need three times dump cycle is that Amanda spreads out level 0 (full) backups across the dump cycle, and this ensures that you always have at least the most recent level 0 backup for any DLE. > > > 2. With current settings, tapecycle and dumpcycle you will have > between 2 and 3 full dumps per partition "on tape" at any one > time, 2.x X 50 Gig >> 80 Gig so you are already short on (vtape) > space. > > Correct I think I also think I am short of Vtapes. I wonder if I > should add more 4.xx G size tapes or redo Vtapes of 40G size each to > utilize whole 300GB of disk space. I use tapes of 10 G and find that a convenient size. I also set runtapes to 2, but be warned that that introduces a new and potentially messy factor into your tape requirements calculation. I also set tape_splitsize to 900 mb, which splits up large dumps into smaller chunks. 11of them will barely fit onto a 10 G vtape, so I get maximum use of each one. > > 3. I believe that vtape size is an upper bound, unused space on > the vtape is actually free space on the disk, so you can actually > oversubscribe the 300 gig pool by some percentage (depending on > numerous factors that we currently do NOT have a handle on). Correct, and I have not looked into the calculation. > > I am not sure I understand what oversubscribe actually is but I > wonder if I really need it. could you tell me what it will actually > do in my case? Let's say you have 25 4 G tapes, for a theoretical supply of 100 G, so you give Amanda a partition of 100 G. But you notice that the runs tend to under-use each tape, by an average of 10%. So you are actually using 90 G. You could (in theory) add two more tapes to that partition. I recommend against it; I prefer to play with the tape size and tape_splitsize to make things better emulate tapes. > > 4. With 4 Gig tapes... how large are your DLEs ? 4 Gig is relatively > small, are you using tape spanning or are all of the DLE's small ? > > I don't believe Tape spanning is configured. I just used Vtapes > document from Amanda wiki and so used 4GB dvd size as it is > mentioned there. Are you planning to back up vtapes to DVD? If not, I'd say, don't worry about the 4 G size and pick something that suits your data set. -- Charles Curley /"\ ASCII Ribbon Campaign Looking for fine software \ / Respect for open standards and/or writing? X No HTML/RTF in email http://www.charlescurley.com / \ No M$ Word docs in email Key fingerprint = CE5C 6645 A45A 64E4 94C0 809C FFF6 4C48 4ECD DFDB
