Re: Veritas volume manager & OnLine
At 01:14 AM 7/27/95 GMT, Michael Loftus wrote: >Greetings! > >I am hoping that someone out there has some experiences to share >regarding the use of the Veritas volume manager on a Sparc >storage array with OnLine 7.1. > >The use of the volume manager has several big advantages from an >administrative standpoint. I'm in the process of getting things >set up and am about to begin some experiments of my own. > >I'm wondering if Veritas obscures information from OnLine >regarding the physical devices the data is placed on to the point >where the effectiveness of PDQ is greatly reduced. In other words, >will OnLine realize that a number of logical volumes (mainly simple, >non-striped ones) are actually from separate physical devices so >that the appropriate number of threads are created for parallel >queries? Is it better from a performance standpoint to let OnLine >manage the disks and forget about using a volume manager? > >Any and all wisdom greatly appreciated. Michael - I can't speak to Sun's LVM since I run Sequent, but they all operate fairly similar. Addressing your questions, OnLine does NOT know what the LVM has done, as far has splitting physical disk into many logical volumes, or many physical disks making up one logical volume. OnLine see only the unit you provide it, which is the logical volume. So you can see that, when using LVM's with vers 7.x of OnLine with PDQ, if you are not VERY carefull, you can in fact shoot yourself in the foot (performance wise). What I suggest (I'm running 7.1 on Sequent, using Sequent's LVM), is that you DO use the LVM to manage your disks. LVM's are much more flexible and powerful, as far as disk management goes. I use the LVM for all mirroring as well. Some may say that OnLine's mirroring yields better performance, but I opt for more flexibility and functionality from the LVM. I typically create 1 or 2 logical volumes from any one disk, being carefull what tables/data gets placed in each. You can create logical volumes comprised of multiple physical devices, but again be carefull what gets where. The idea is not to let the LVM complicate your data layout any more than possible. I'm a strong believer in LVM's, but when trying to exploit PDQ, you need to be careful how your data gets layed out. Jon ================================================================== Jon Vemo Internet: jvemo@cyberspace.com Bothell, WA USA ------------------------------------------------------------------ Watch out for road-kill on the information superhighway....SPLAT!! ==================================================================