Re: HP9000+LVM+Online

mikehunt@algonet.se wrote: > By taking the four disks that we were spreading > the database over and turning them into one disk consisting of alternating > 1Mb chunks of disk we were able to totally remove our disk bottlenecks > and realise a 30% increase in system throughput. The more I think about this the more I can't see how this could have been the best option (although obviously you're there and I'm not, so...) Given that your application is very update-intensive, you would want to take the most possible advantage of the fact that page cleaners do sorted writes during a checkpoint. The traditional sound advice of: no. of disks = no. of chunks = no. of page cleaners - is very sound and tried and tested: at checkpoint each page cleaner grabs a disk and does sorted writes to it. Easy. With alternating 1MB chunks in each logical volume, they'll be switching from disk to disk the whole time and there's a good chance you'll sometimes get more than one page cleaner thrashing one another for the same disk. The only way to completely prevent this would be to configure just one page cleaner - which of course then becomes a bottleneck in itself. If there was a lot of read-intensive activity from one big table as well, then you could always spread its dbspace across Online chunks on different disks. Maybe on the read side your striping method has some advantages, but I can't see how it can do anything but harm you on the write side. But as ever, I'm open to being proved wrong. akent@cix.compulink.co.uk (Andy Kent) -------------------------------------