Re: raw devices - general questions
In article <55la96$jia@cssun.mathcs.emory.edu>, Billy Wheeler <billy@west.co.za> writes >> I have 2 4-gig SCSI drives (one for a primary, one for a mirror) that >> I want to configure as raw devices for Informix 7.13UC1 - a data >> warehouse. >> >> what exactly is the offset that informix is asking for when I create >> my dbspace and initial chunk? Is it in tracks? Is it the number of >> tracks to skip before writing data OR the track number to start >> writing at??? >> I think the SCSI drive has a table of contents/VTOC at track 1, which >> I obviously want to leave alone. Would my offset be 1 or 2?? > >The offset is in Kilobytes, so you would probably want to play safe and leave >100K or so free... Correct the offset is in kilobytes (Informix Online Dynamic Server Administrators Guide, Volume 2 Version 7.1 Page 38-54, under ROOTOFFSET). This covers the root chunk, the others are the same. The offest required varies between Operating Systems and even between version (Solaris 2.4 was 4K(?) and Solaris 2.5 8K). The value required also changed if you use a Logical Volumn Manager (LVM) which you will need to do - see below. I would talk to the Operating System vendor. With all respect to Billy, 100K is really a big guess (it's also the value I normally use but that is only on new machine which is not in a live enviroment and if I totally screw up there is no harm done! 100K has always worked for me but some Operating System may exist where it will not work). Check with the Operating System Vendor and mention that you will be using a Logical Volume Manager. > >> I was hoping to create two 2-gig chunks on the drive. Because >> Informix has a 2-gig chunk limit, does this mean that it can't access >> or "go past" the first chunk on the drive??? Will my second chunk be >> available? If so, how do I calculate the offset for the 2nd chunk?? > >No, it will read 2 x 2GB chunks on a 4GB drive, the offset for the second >drive will be offset of first drive + size of first drive. > >HTH. > Sort of Informix can not access any part of the drive beyond the 2 gigabyte limit. This is because it uses the lseek() system call which only allow you to move to a postion up to 2 gigabytes into the drive. Therefore you need to use a Logical Volume Manager (LVM) to split the drive into what appears to be 2 x 2Gb) drives. Rather than one entry in /dev for the drive you will have two entrys in /dev one for each Logical Volume. Also be aware that if you are using ICL's Logical Volume Manager you will need to disable Informix Online's Kernel Asynchronous I/O feature by setting the environment variable KAIOOFF to 1 before you start Online 7.13. If not you will probably get data corruption (we got the Unix root partition (/) corrupted so bad it was not recoverable and we had to restore the complete machine from backups). This happen to us 4 times before Informix admiteed a problem... PS No part of this posting may be used by Oracle marketing people. I'm not having Oracle quote my Usenet posting as they have done to other people. Copyright David Williams 1996. -- David Williams