RE: Raw devices are a thing of the past

CONCLUSION ---------- >Raw devices provide the greatest i/o thruput becuase they bypass the buffercache. Amongst other things, they also bypass all the vfs i/o handling. >Raw devices are not as easy to maintain for a dynamic system than cooked files. I disagree, on large systems you have to have some sort of LVM, I find these just as easy to use with cooked or raw. >Cooked files are slow because they go theu the buffercahce. They are also slower 'cos compared to raw there can be a significant amount of code between the request and the disk access >Priority paging can help this, but only to a degree. True, this has been around since 2.5.1, and is always off by default. >Mounting a f/s holding cooked db files with forcedirectio gives you most of the >benefits of using raw space, without the drawbacks. It removes the caching issues but doesn't get round the overheads associated with th FS i/o. I was at a discussion group late last year held by one of the Sun performance gurus. He stated that he could be FS i/o faster than raw but only by using two directions striping ie, striping across the disks and then striping across the stripes. The disadvantage was it was a totally nightmare to add more disks I would also add if the page daemon is at the point of having to steal pages then you haven't got enough memory, or at least there is a periodic shortfall. All the tweaking in the world will not generate memory from nothing >Thanks for your time in reading this ! :) It took a while :-) Paul Watson WF Software Ltd Tel: +44 1436 674729 Fax: +44 1436 678729 www.wfsoftware.com # If you broke it, hide the evidence ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com **********************************************************************