On Fri, Mar 4, 2011 at 1:10 PM, John Hanley <[email protected]> wrote:
> I'm looking to use the new XIV box to for DB2 space in a DB2/WebSphere > environment. > The I/O and channel utilization currently is not a problem, but CPU can be. I thought someone told me XiV would be doing ECKD as well, but I don't see that at all. Maybe the representative in the booth was just tired or defaulted to "yes" like a good sales person :-) Given the XiV, your option would be than native FC or EDEV, right? WebSphere should not be an issue, since it normally does not really do I/O. DB2 might be sensitive to I/O, depending on the type of workload. You should collect performance data and review that. If you want a very rough rules of thumb: I ran a pure I/O workload (with "dd") and EDEV had a T/V ratio 1.5 and ECKD was around 1.1 This sounds bad, but it does not tell you anything unless you know how much CPU your application would spend on I/O. Assume your DB2 server is busy 20% of the time, and during that time is 20% in I/O wait. Add a bit for disk writes (your performance data shows you how much you really write). So it would be doing I/O 5% of the time. Some of that is CPU and some is waiting for the disk. Imagine that is 1:5, this would mean 1% of a CPU is spent to issue the I/O. If CPU is your concern already, it means > 90% of CPU is used for non-I/O related things. So even when CP adds 0.5% on top, it does not really make a lot of difference. The difference obviously does show in synthetic lab experiments, but how many of us run those as their normal workload. It's a poorly kept secret that I can often be talked into reviewing performance data... Rob -- Rob van der Heij Velocity Software http://www.velocitysoftware.com/
