Douglas Ritschel Douglas.Ritschel@fnc.fujitsu.com writes:
I just got back from "NetApp 202 Advanced System Admin & Troubleshooting" class. They went over a similar scenario. They had two volumes, one on each of two controllers. (they said that there is 10 percent performance hit, when drives in an volume are on different controllers). For example, if they had two volumes, each with six drives, and the all of the drives for the first volume were on the first controller and all of the drives for the second volume were on the second controller. And then a drive failed in the second volume, and rebuilt on a spare on the first controller. There would be a 10 percent performance hit, every time you accessed the second volume.
and Bruce Sterling Woodcock sirbruce@ix.netcom.com elaborates: | | Unless I misunderstand some of the bus issues involved, the 10% | performance hit would only occur on writes, and since writes are grouped | and it is unlikely that you are writing to the drives ever second, you'll | never notice it. | | Reads come off individual disks as needed, so it doesn't matter which | controller they are on. (I guess if you needed to read a whole stripe at | once there's a potential hit, but I'm not sure that necessary.) The point | is, with two volumes you're using both controllers anyway.
I'm a bit surprised to see the performance penalty, small though it may be, be this way around. I would have assumed that spreading the disc I/O load across controllers as much as possible would be the right thing to do. Can someone explain this seemingly counter-intuitive result in more detail?
Incidentally, the original poster talked only about separate shelves, not separate controllers. If by this he meant two shelves on a single FCAL loop (he didn't say whether his discs were FCAL or SCSI), would the above still apply or not?
Chris Thompson University of Cambridge Computing Service, Email: cet1@ucs.cam.ac.uk New Museums Site, Cambridge CB2 3QG, Phone: +44 1223 334715 United Kingdom.