Re: How does TAPESIZE in onconfig work?

Steven L Cooper wrote: > > My system has a SCSI 4GB DAT tape drive in it. > > Informix tech support told me to set the number to 400000 (FWIW). > > I was "testing" the ontape (level 0) program and it filled the first tape > and asked for another! I was shocked that it took two tapes. On a guess I > doubled the TAPESIZE option in the onconfig file... > When I ran ontape again (level 0) it completed on ONE tape!!! > > My question is: What is the TAPESIZE number referring too? > Steve > > my onconfig.ows now... > TAPEDEV /dev/rStp0 > TAPEBLK 16 > TAPESIZE 800000 TAPESIZE is the data capacity of a single tape (or tape set for tape arrays) expressed in 'K'. The "recommended" value of 400,000 tells the archiver to stop writing to the tape once 400MB of data has been written and ask for another set of tapes. This should have been 4,000,000 or 4GB assuming that the 4GB capacity you quote is uncompressed capacity and you are writing to the tape without compression (if so with compression enabled on the drive you will be able to get between 6-8GB per tape). Informix archive products do not detect EOT (except as an abort exception, this has historical roots in older UNIX systems which did not properly detect and report EOT conditions) it will write only TAPESIZE K to the device and stop. Conversely, if TAPESIZE K do not fit on the tape and a hard EOT is detected the archiver will abort! This means that you must be careful to not overestimate compressed capacity (different data will compress at different rates). Compression should be at least 30% (increasing capacity by 50%) but not much more than 50% (doubling capacity). I hope that this is what you need. Art S. Kagel