PE R910 and two MD3200

We have an R910, with an MD3200, full of SAS 600GB dirves, with 4 connections to a pair of SAS6G card., and another MD3200 full of SAS 2TB drives, with 4 connections to a pair of SAS6G cards - so we have 4 SAS6G cards in the server. The 2 SAS6G cards for the MD3200/2TB are in slots 8 & 9 (so on IOH1), and the SAS6G cards for the MD3200/600G are in slots 2 & 3 (on IOH2).

 

Running some IOMeter tests, we get 2400MB/sec when we test the MD3200/2T on its own. When we test the MD3200/600G on its own, we get 3100MB/s. However, when we test both together, the speed tops out at around 3500MB/s.

 

We're really confused about why this is happening, as are tech support, who have now decided that this is a performance tuning issue that they can help no nurther with.

 

The real issue we're having is not the speed of each of the MD3200s - in isolation, the speeds are acceptable to us. The problem is that when we run both MD3200s together, the speed of around 3500MB/s about 60% of what it should be. We're no where near the limit of the PCIe slots, and each of the MD3200s is on a seperate IOH, so we shouldn't be saturating that.

 

Does anyone have any ideas why things are not adding up?

Does anyone have a pair of MD3200s connected to an R910? If so, what aggregate speeds are you getting? And is it the sum (reasonably) of the individual MD3200s?

 

As I said, I am not overly concerned about the absolute speeds (2400MB/s and 3500MB/s are fine), it's the fact that when running both boxes together, we are getting such poor performance.

 

 

Graham