Interesting. I have a different question related to the same issue of I/O on 10gR2 AIX. I wonder if anyone else on this platform can tell me whether you've seen anything similar. I have observed about a 10x difference in throughput for direct-path reads vs multi-block reads of the same size. In other words, as soon as a query switches from multiblock to direct path, it suddenly does I/O literally 10 times faster. I expect direct path to be faster (bypassing buffer cache overhead and all), but this seems a bit extreme! I'm curious about others' experiences with direct path reads - has anyone else seen this big of a speed difference between direct path and multiblock? At one point, full tablescans were pulling table data at about 16MB/s with direct path and about 180MB/s with direct path. I haven't started digging yet, but does anyone know if these two methods use the same system I/O call? If so, that might indicate something in the database accounting for the difference, otherwise it could be a combination of DB and OS. At the storage tier, these tests were reading the exact same blocks. I alternated between them several times to make sure I wasn't just seeing cache interference. Also, I was calculating these throughput number from the wait events... and I didn't see any wait events related to contention. All the wait time was "db scattered read" or "direct path read" - both reading 32 x 16k blocks per wait. -Jeremy On Wed, Aug 3, 2011 at 9:59 AM, joshuasingham <joshuasingham@xxxxxxxxx>wrote: > Hi , > > I been looking at some (10.2.0.4) on AIX 64 bit Awr report File IO Stats > and can see that the Av Rd(ms) for some of the files are consistently above > 50 to 60 ms over a 15min interval but when I reported this storage guy he > mention and sent me the Iostat to prove that the service time in the same > timeline is average of 20ms for the disk involve . What can cause the > difference between the AWR and iostat readings > > thanks > -- http://www.ardentperf.com +1 312-725-9249 Jeremy Schneider Chicago