Re: Informix data fragmentation or RAID disk

Charlie Sadler (charlie_sadler@mathworks.com) wrote: : Also Informix 7 supports read from mirrors. So if you : have two disk arrays, one for the primary and one for the mirror, each on : its own disk controller, you have two possible channels for any given : read. If one channel (disk and controller) is busy, the database can go : to the other in order to satisfy the read. Redundant read paths is : perhaps why Informix recommends database mirroring over hardware : mirroring. The database server has no way of knowing if a channel is busy or not. When a chunk is mirrored, we essentially split read requests across the 2 based on physical location of the page. A page in the first half of a chunk will be read from the primary and a page from the second half from the mirror. If you are after optimized reads from a mirrored environment, you will have to go to hardware mirroring to get it. "Informix" does not recommend either mirroring method unconditionally - we will recommend one or the other based on the circumstances of the setup and the customer's needs. Dave Kosenko Disclaimer: All opinions expressed in this message are well-reasoned and insightful; needless to say, they are not those of Informix Software, its partners or lackeys. Anyone who says otherwise is itching for a fight. **************************************************************************** "I look back with some satisfaction on what an idiot I was when I was 25, but when I do that, I'm assuming I'm no longer an idiot." - Andy Rooney