On Mon, Jan 17, 2011 at 05:17:26PM -0500, Robert Heller wrote: > We are running Amanda 3.2.0 on three CentOS 5.5 systems. > > We have one large (1.5TB total) file system for data (/data), three > 100meg /boot file systems (one on each machine) and three ~100G root > (/) file systems (one on each machine). > > We are using a 2TB USB disk for backup storage, with a disk-based > (virtual) tape changer. The tape changer is set up to have 200GB > 'tapes' with a chunksize of 50GB. We are using a 7-day backup cycle and > are using 1 tape per run. > > Amanda does a full backup of the /data on one day of the week and then > does level one backups for the rest of the week. It does a level one > backup of the other 6 disks on the day it does the full of /data, and > then does full backups of the other 6 disks on the other 6 days. > > Why does Amanda make so many full backups? Is there a configuation > parameter we need to set to change this?
Amanda tries to level out, or "balance", the amount of data sent to tape each day of the seven day dumpcycle. The mechanism it has to achieve this balance is to "bump" a DLE to a higher level (reducing the amt of data sent to tape) and "promoting" a DLE to level 0 (increasing the amt of data sent to tape). The balancing act works quite well in configurations with a lot of varied DLEs or with only a few similarly sized DLEs. It falters in configs, such as yours, with only a few DLEs and a couple of widely different sizes. Making a few assumptions for an example, your file systems at 1/3 full, changing that data 5%/day, no compression, ignoring your small /boot file systems. So you would have 500GB in /data + 100GB total in the 3 root file systems, 600GB total. Amanda will attempt to tape 90-100GB each of the 7 runs. On the day /data gets a level 0 (500GB) amanda bumps everything it can trying to get as close to that 100GB "balanced value". On the days /data gets a level 1 or greater, its dump contributes only 20 or so GB to the daily total. Level 1s of the 3 root file systems would only increase this by about 10GB. So amanda promotes what it can to get close to that 100GB/day taped data number. /data won't be promoted so the /'s are. As Toomas noted, you can apply constraints on amanda with the 'maxpromoteday' setting. Bumping (not your problem) can also be fine tuned with several "bump" settings. Another approach is to split the /data DLE into several smaller DLEs. Each of these DLEs would start at /data but with 'include' and 'exclude' settings would only deal with a portion of the file system. Jon -- Jon H. LaBadie [email protected] JG Computing 12027 Creekbend Drive (703) 787-0884 Reston, VA 20194 (703) 787-0922 (fax)
