Re: HP9000+LVM+Online

Andy I got the impression that Mike's system only had one chunk (therefore one page cleaner) which was striped underneath using LVM. Note that LVM is pure striping where one logical write equates to one physical write therefore it doesn't suffer the write penalty found on RAID. In general, this would (theoretically) quadruple read throughput i.e. given a long random list of read requests, it would get through them four times quicker. For writes, the application inserts 250,000 times (20%) and updates 1M+ times (80%). Again, LVM would mean that updates are quicker because reading the record + index leafs would be faster. For sorted writes, you will still get a sorted write on each of the underlying disks. e.g. if we have a 2 disk LVM, and Online writes pages 1 2 3 4, this would translate to disk1page1, disk2page1, disk1page2, disk2page2. As you can see, the actual physical write to each disk is sorted. The only thing I'm concerned about is that some LVM products don't do synchronous writes i.e. it buffers them. If this is the case on HP then beware, because a checkpoint would not actually write to disk. David W Chan Objective Research Ltd dwc@cix.compulink.co.uk