Re: TAPE BLOCK SIZE

cherylk@prod1.jcdc.doleta.gov (Cheryl Kendricks) wrote: >I am running tbtape from UNIX 3.2 and Informix 5.X engine on IBM RS6000. I >have a 10GB database and am using 5.0 GB IBM 8MM Tape Drive. It takes 4 <...snip...> >So smart me changed it to 960 hoping it would at least get to 2 hours, if not >one. BUT NO It went back to 4 and used more tapes. Cheryl, It seems to me that you are telling Informix to write 2.25GB to the drive in one blocking operation (960*245760/1024**2). Have you correctly identified the drive to Informix as a 5.00GB drive? See your tbconfig. There are three components to be looked at: 1) The "physical" block size of the tape drive. You can set this through SMIT, but the only useful value for an 8mm drive is 1024. If it is set to 512, the remainder of the 1024 is padded with nulls, NOT DATA. This wastes half the tape and half the time. 512 is only used for installation of the AIX Base Operating System (AIX will only boot from a 512 block size tape) 2) The blocking factor (how many blocks at a time) Informix should use when writing to the drive. 3) The block size Informix should use, which must be a multiple of the tape's own block size. 1 has to be right. 2 & 3 should be adjusted to fit the tape, but YMMV depending on how much memory your system has. From memory, 10GB in 3 hours sounds about right for a single drive without hardware compression. I would be stunned if you could get it down to 2 hours. Don't be misled by "marketing" claims for peak transfer rates. Sorry I have no magic cure. > Cheryl Kendricks Regards Tony da Franca -- +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + Tony da Franca, Hewlett Packard UK + + Any views expressed are my own, not Hewlett Packard's + + E-mail: tony_dafranca@hp-unitedkingdom-om7.om.hp.com + +++++++++++++++++++++++++++++++++++++++++++++++++++++++++