On Thursday 12 June 2003 09:41, Bill Nolf wrote: >First time - setup. > >I have a HP-DAT 40 that should get 40GB with hardware compression. > >I ran amtape type and got the following. > >length 16534 mbytes >filemark 0 bytes >speed 2570 kbytes > >Does this look right? The first run didn't come close to 40gb or > even 20gb. > >thanks, Bill
With hardware compression on, the output of /dev/urandom overwhelms the compressor, and the data will expand such that what you see above as 16534 megabytes will be about 20,000 megabytes by the time its actually *on the media*. This is the main reason most of us are so adament about turning off the hardware compression and using the software compression where its appropriate. gzip can beat the hardware quite handily when run at its 'best' setting against those disklist entries that contain compressible data. OTOH, a directory full of tar.gz's and rpm's is not compressible, so use a non-compressing dumptype for those and save lots of time. Its another good reason to break your disklist entries up into subdirs such as /usr/local, /usr/share, etc etc. Each of those directories will contain a different style of data. Compress them all at start time and look at the email, if a level 0 of that entry didn't compress more than 10%, or maybe even expands (compression reported as 107% for instance), don't waste the time trying. With hardware compression on, amanda has no idea how much tape is left because of this internal processing the drive does, so you have to make your tapetype smaller than 40Gb to compensate, by about the ratio you saw above. With it off, and the tapetype set to the tapes uncompressed capacity, then amanda can keep track of how many bytes has been written to the tape quite well, and make use of all the tape if she can and needs to. Following the above outline, I have occasionally seen amanda put more than 10 gigabytes of "from the disk" data on a single DDS2 tape, nominally 4 Gb. I would expect similar ratios from a 20Gb DDS4 tape under the same conditions which could theoreticly hit 50Gb of raw data on that 20Gb tape. Under admittedly ideal conditions... YMMV of course :-) -- Cheers, Gene AMD [EMAIL PROTECTED] 320M [EMAIL PROTECTED] 512M 99.26% setiathome rank, not too shabby for a WV hillbilly Yahoo.com attornies please note, additions to this message by Gene Heskett are: Copyright 2003 by Maurice Eugene Heskett, all rights reserved.
