On Wed, 9 Jan 2002 at 4:40pm, Dengfeng Liu wrote > Can anyone here tell me the difference of software compression,hardware > compression and tape capacity? > For example, I have a sony AIT2 autoloader(can anyone give a chg-scsi > configuration file?),which have 50GB(native)/100GB(compress) mark on it.
In general, ignore manufacturer's claims of compressed tape capacity. Your tapes hold 50GB of data. > also, the autoloader have a hardware compression switch.If in my > amanda.conf file I use compress high,then the tape can hold 100GB tar.gz > file of the amanda output?if the software compression ratio is 30%,then > can I run a backup of a file system size of 140GB if I open the hardware > compression switch? *Never* use both software and hardware compression -- trying to compress (in hardware) already compressed (in software) data will result in the data actually getting much bigger. > In one word, I am totally confused with the 50GB(native)/100GB on the tape > and the compression option in amanda.conf. > There was a thread this morning about software vs. hardware compression -- check the archives. Pick one or the other. Software compression puts more load on your CPUs, but lets amanda more accurately assess tape usage (since it will know the precise before and after sizes of the compressed images). Hardware compression will speed your backups and take the compression load off of your clients/server, but you'll have to lie to amanda in the tapetype about your tape capacity, and that lie will be a guess as to the compressed capacity of your tapes. And it *won't* be 2*native capacity. I use AIT1 tapes (35GB native), and can get about 50-55GB on them using hardware compression. YMMV depending on your data. -- Joshua Baker-LePain Department of Biomedical Engineering Duke University
