> -----Original Message----- > From: [email protected] [mailto:owner-amanda- > [email protected]] On Behalf Of Gene Heskett > Sent: Wednesday, July 07, 2010 11:33 AM > To: [email protected] > Subject: Re: Tape Usage Question > > > On Wednesday 07 July 2010, McGraw, Robert P wrote: > >> -----Original Message----- > >> From: [email protected] [mailto:[email protected]] On Behalf Of > >> Dustin J. Mitchell > >> Sent: Wednesday, July 07, 2010 1:14 AM > >> To: McGraw, Robert P > >> Cc: [email protected] > >> Subject: Re: Tape Usage Question > >> > >> > >> On Tue, Jul 6, 2010 at 11:56 PM, McGraw, Robert P > <[email protected]> > >> > >> wrote: > >> > In my case there were several dump image that could have been > written > >> > >> to the tape. Amanda did not seem to pick the largest dump image that > >> would fit on the tape. > >> > >> Well, bear in mind that the tape drive does not give any indication > of > >> space left -- all Amanda has to go on is dead reckoning based on the > >> parameters in the tapetype and what it has written so far. So if > >> Amanda chose the 37GB dump, it probably expected at least 37GB > >> remained on tape at that point, although you knew better. Are your > >> tapetype parameters correct? > >> > >> Dustin > >> > >> -- > >> Open Source Storage Engineer > >> http://www.zmanda.com > > > >[McGraw, Robert P] > > > >Dustin, > > > >I use an LTO-2 drive which is supposed to give 200GB uncompressed and > > 400GB compressed. I realize that the 400GB is the absolute max and > would > > never be obtainable. So I make tapetype equal to a pretend 350GB > which > > seems to be a good number. So to amanda it thinks that the tape size > is > > 350GB and bases it calculations on this number. > > > >define tapetype LTO2-HWC { > > comment "LTO-2-Hardware Compression on." > > blocksize 1024 kbytes > > length 350000 mbytes #350G compressed > > filemark 0 kbytes > > speed 27315 kps #27 Mb/s > >} > > > Humm "Hardware compression on". So amanda has not even a SWAG clue as > to > what the tape will hold. If you are also doing software compression, > using > such as gzip, please bear in mind that gzip can do a much better job of > it > in many cases than the hardware compressors can, AND that there is a > high > probability that a gzip'd file, already having been compressed, will > actually grow, sometimes quite a bit, in that hardware compressor. > > This is saying that it is generally bad kharma to use both. The choice > is > tipped very quickly and positively to the gzip method, with the > hardware > compressor turned off by the fact that amanda now knows exactly how > many > bytes have been sent to the tape as it tracks the size of the gzip'd > output > file. And the best-fit works as expected. > > Be aware that turning off the hardware compressor can be a frustrating > experience because the state of the compressor is usually stored on the > tape, in a data block at the beginning that is over-written each time. > The > problem with that is that if it is enabled, then regardless of your > commands > to disable it, it will be re-enabled from this hidden header each time > the > tape in inserted and re-read by the drive so the drive can configure > itself > to that exact tape. > > And amanda re-does this tape recognition sequence in checking the label > on > the tape, forcing the hardware compressor on if that flag bit is set. > > I only know of one foolproof method to turn it off in that case and it > doesn't use amanda to do it: > > 1. Insert the tape, make sure it is rewound. The drive will generally > do > this in recognizing the tape. > > 2. Using dd, read out the first block containing the label and save it > to > disk. > > 3. Rewind the tape with mt. > > 4. issue the command to disable the hardware compression, probably > using mt. > > 5. re-write that label block file using dd. This will re-write that > hidden > block too, turning the hardware compression off for this tape, and it > also > effectively trashes the rest of the tape, rendering it unreadable. > > So it must be treated as a new tape in every way but the use count if > you > are tracking that. From this point on, the hardware compression should > be > off, and you can use amanda's housekeeping utilities to re-label the > tapes, > and that should be done so amanda knows it is losing its database as > you > amrmtape, and amlabel relabel the tapes. > > I have been known to run a dump 5 or 6 times in a row in the same day > so > amanda will rebuild the database, and the normal backup runs won't > waste > several days doing a level 0 on the whole system, rather than a few > each > night because one tape doesn't have enough room for a level 0 on every > DLE. > Its forcing the issue, but amanda seems to settle into its routine a > lot > faster if I do this. > > >The problem is not the size of the physical tape, the problem is that > > amanda did not pick the largestfit dump image based what amanda knew > to > > be how much was left on the tape based on tapetype length size of > 350GB. > > > > > >1) amanda knows the tape size based on tapetype information which in > my > > case is 350GB. > > > Reset this to 200GB, the true size of the tape. > > >2) amanda knows the amount of data the is written to tape. You can see > > that in the amreports and amstatus information. > > > >3) amanda knows how much disk spaced is left of the 350GB and from > this > > number amanda should get the largestfit dump image that is less than > the > > disk space left. In my case amanda picked a dump image that was > bigger > > that the disk space left. So as the templar knight said in the > Indiana > > Jones "The Last Crusade" amanda "did not pick well". > > > >Oh well I do not want to beat a dead horse. > > And the above advice should revive the horse. ;-) > > >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) > The nation that controls magnetism controls the universe. > -- Chester Gould/Dick Tracy [McGraw, Robert P]
Gene, Thank for the information. I only use hardware compression, no software compression. When I tried software compression it was taking way to long. Thanks again Robert
