Active-Active Arrays (aka XP/Hitachi) and VxVM DMP - dual paths or multipaths to every LUN?

[Alzhy]

I am now a bit confused which would be the most optimal configuration (performance and growth). Assuming my environment has 8 Fibre-Channel HBAs (i.e. XL2) and and say 256 LUNs, which would be better?

1) 64 LUNs in each pair of XL2s (dual path)

or

2) 8-Paths to each 256 LUNs and just have DMP do tis thing?

Let's also assume, the system is fully VxVM licensed (DMP enabled) and Array Support Library (ASL) for the specific model/brand is used/implemented...

[Christopher Rupnik · Accepted solution]

Hi
We had a similar setup to yours and we chose option #2. It was a mistake. Throughput is much better after we switched to option #1.

We believe it is because if you chose option #2, the IO is broken up by DMP, and the XP spends too much time putting it all back together. If you do option #1, then the XP spends almost no time "putting the io back together"

Now IO times DO go up with option #1, but throughput is better. The numbers only give part of the story. This was a large Oracle database implementation

You might get a lot of theoretical responses, you can choose to listen to what you will, but this was pratical experience, which for me is always more valuable

[Alzhy]

Chris, thanks for sharing your experience.

I wonder if those runing AutoPath (aka SecurePath for Active/Active arrays) are facing the same dilemma.. i.e. for Autopath to just do the path decisions when dealing say with 8-paths to every XP or EVA4/6/8K LUN presented.

[Christopher Rupnik]

The issue is what DMP does. Any product will have the same issue if it performs truly distributed pathing, like DMP Does. DMP In VRTS 3.5 performs sequential path selection. First chunk down path 1, second down path 2, round robin like that.

With VRTS 4.0 and products like autopath/securepath, then you have preferred path, which will send more chunks down the path with the shortest queue lenght, etc etc, which might make things better or might not. Those I do not have pratical experience with.