On Tue, 2004-05-18 at 10:14, Joe Konecny wrote: > Am I correct in thinking that if I am backing > up only the server running amanda then it makes > no sense to use the holding disk?
Not exactly. If you are backing up files from the holding disk, for example in other directories, then it probably makes no sense to use the holding disk. For filesystems other than the holding disk, you may still get better tape performance by using the holding disk because dumps may stream to tape better than dumping directly to tape. Offhand, I'd say use the holding disk. If you really care, then try it without the holding disk and compare the statistics with and without using the holding disk. In a nutshell, the 2 questions are: 1) How fast does your tapedrive gobble up data? 2) How fast can the backup process feed data to the buffer(s)? The goal is to keep the tapedrive "streaming" as much as possible, which means keeping a full buffer, which means your backup process better generate data faster than the tapedrive can absorb it. Otherwise, every time the buffer goes empty, the tapedrive has to stop and reposition, which takes time and may eat up space on the tape, making for slower backups that use up more tape to store the same amount of data. If the amanda server is the only client, I'd probably turn on hardware compression on the tapedrive, turn off software compression, and maybe dump directly to tape. If there are other clients involved, and you want the bandwidth savings of software compression client-side (which I do) then I'd stick to software compression for everything and use the holding disk on the amanda server, since the software compression would slow down the backup process and increase the chance of emptying the buffer. Why then use software compression for everything? I'm not sure if it's a good idea, or necessarily possible, to mix hardware compressed and uncompressed data on the same tape, or to get amanda to somehow switch the tapedrive between those modes. I am sure that applying hardware compression to data that is already software compressed will use at least as much, and probably more (and possibly a lot more) tape. -- Jonathan Dill <[EMAIL PROTECTED]>
