AW: Ideal disk blocksize for Informix on Linux

Dear Rupan3rd, First of all I'd make sure I don't use RAIDfive,four or aeeh fthree (see www.baarf.com) . :-) For the blocksize - I'd set it to the same as the IDS blocksize or page size. The default page is 2k on LINUX but you may create dbspaces with other pages sizes (new in IDS 10). It can be any whole integer multiple of 2K up to 16k. The page size to use is dependant on the tables you store in these dbspaces. I don't want to give any fixed rules, but the reasoning is as follows: - if the rows size is small and you choose a large pages size (e.g. 16k) you will end up with many rows (up to 255) per page This may not be what you want, as it may result in memory inefficiencies , when you read in 16 k to read one tiny little row and you don't need the rest of the rows. To achieve an acceptabl rate of BUFFERING , you have to create huge BUFFERPOOLS. - if rows size is large and you use standard 2k pages size, you'll probably end up wasting space on disk. For example on a 2K page there is 2020 bytes free for storage (28bytes overhead on each pages) Each row stored on the page creates another 4 bytes overhead on the page. So if your row size is 1007 bytes, you store one row on a page (uses 1013 bytes altogether) and waste 1007 bytes which is unusable. This leads to high waste of disk space and bad buffering as well. So you need to balance this. I'd create dbspaces of standard 2k page size for most tables and decide whether there are some tables in your database that may benefit from a larger pagesize. Create dbspaces with appropriate pagessize and move the tables into that dbspace. I'd separate dbspace file system from other filesystem . Also, i'd separate dbspaces with different paegsize to different files systems and different hard disks. HTH Tilman <This information is provided AS IS etc, etc ... shall not be liable etc, etc....standard disclaimer :-)> -----Urspr|ngliche Nachricht----- Von: owner-informix-list@iiug.org [mailto:owner-informix-list@iiug.org] Im Auftrag von Rupan3rd Gesendet: 15 December 2005 10:01 An: informix-list@iiug.org Betreff: Ideal disk blocksize for Informix on Linux Hi Gurus, I have to install Informix IDS 10 on a Red Hat EL4 box, it's an HP DL 385 with a P600 disk controller which features hardware RAID. When setting the hardware RAID on the 5 disks that I've decided to reseve for the database, I am offered to specify the blocksize (8,16,32,64,128 Kb). AFAIK Informix default block size is 16Kb, should I set the DB volume blocksize accordingly? What if the volume containing the Informix dbspaces contains also some (non-OS) filesystems, is the impact on filesystems' performance significant? Any experience about this? Thanx in advance Rupan3rd (from Italy) sending to informix-list