Re: Veritas volume manager & OnLine

In <3v6pa8$30d@usenet.interramp.com> Michael Loftus <mloftus@interramp.com> writes: >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. >Thanks, >Mike >Michael Loftus mloftus@interramp.com I am not familiar with Veritas' product but I hope it won't matter. I recall a discussion in the last NYC user group meeting about this topic and the general notion is greater awareness can, on the average, yield better performance. The usage of a logical volume manager may hide the very details that the engine should have for making good decisions. But, I think you are confusing threads and i/o requests. The idea of a PDQ query is to distribute a single query across processors, not disks. On the other hand, the use of a lvm may clash with table fragmentation since they operate on different levels of abstraction. I hope this helped. Edwin Babadaglian edwinb@panix.com