On Wednesday, August 24, 2011 05:13:46 PM McGraw, Robert P did opine: > Gene, > > Thanks for your information. > > I tried the gzip way but it took too long on my backup server. My iron here is beginning to took toward collecting SS one day, but it was good when I built it from boxes of parts about 4 years ago. Quad core Phenom running at 2.1Ghz, 4Gb of DDR2 ram. Today that isn't much to brag about. A typical run here grabs 2 boxes for 36 DLE's, and is done in a long hour most nights, backing up a bit less than 30Gb most runs. To vtapes on a 1Tb drive.
> With my old LTO2 drive I took 90% of the compressed value and used that > as the length. With "device-property "LEOM" "true"" and part_size > 40GB, I was getting close to filling my tapes to 100%. > > If I ever get a faster backup server I will retry the gizp way again. > > Thanks again, > No problem Robert, but I did need to emphasize the 'price' of the trade offs. ;-) > Robert > > > -----Original Message----- > > From: owner-amanda-us...@amanda.org > > [mailto:owner-amanda-us...@amanda.org] On Behalf Of gene heskett > > Sent: Wednesday, August 24, 2011 10:43 AM > > To: amanda-users@amanda.org > > Subject: Re: Do you use this library > > > > On Wednesday, August 24, 2011 10:17:33 AM McGraw, Robert P did opine: > > > JF, > > > > > > > > > Recently you sent me your tapetype for an lto4 drive. I have a > > > question about the length parameter. > > > > > > An lto-4 tape has a non-compress length of ~800GB and in compress > > > about double. I know these are max values. > > > > > > In you answer below you have length set to ~772GB. If I am going to > > > run in compress mode so should the length value be double or > > > ~1.4TB. > > > > You cannot double compress in normal practice. Feeding a highly > > compressed > > file to the lightning fast compression methods used in tape drives > > will often result in the file growing larger by many percentage > > points. > > > > Gzip can generally beat the tape drives at their own game, albeit at > > the expense of cpu time to do it right. > > > > There are also pretty valid arguments against using the drives > > compression as it isolates the backup program, preventing it, > > regardless of the name of > > the program in question, from keeping track of how much of the tape > > has been used since the best the programs can do is count the bytes > > sent down the cable to the drive. If the drive is massaging the > > data, shrinking or expending it, then the program has no real clue > > when the tape is full till the drive reports EOT. > > > > Because of these considerations, it is pretty universal here that the > > recommendation is to turn off the drives compressor and let software > > methods do the data smunching. Then amanda, or any another other > > program that does track the tape capacity, will then know how much of > > the tape has been used. > > > > This can be very difficult to actually do for those tape formats, most > > of them, that record the compressor's state in a hidden header file > > we never see. DDS is one such format where you will have to write a > > script that: > > > > dd reads the first block of the tape out to a file, then > > mtx re-winds the tape, then > > mtx turns off the drives compressor, then > > dd re-writes the first block of the tape with the saved file > > > > All without ejecting the tape or going through a tape recognition > > cycle as most drives do for a freshly inserted tape, and which would > > turn the compression back on despite your wishes. Only a similar > > operation will actually turn it of for most drives today if it has > > ever been turned on and > > the tape written to. > > > > You can of course ignore this advice Robert. > > > > > Thanks > > > > > > Robert > > > > [...] > > > > Cheers, gene > > -- > > > > "There are four boxes to be used in defense of liberty: > > soap, ballot, jury, and ammo. Please use in that order." > > > > -Ed Howdershelt (Author) > > > > He's dead, Jim. Cheers, gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) The covers of this book are too far apart. -- Book review by Ambrose Bierce.
