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July 13th, 2012 00:00
CX v's VNX back end bus question
Can someone, in simple terms, give a good explanation of how the back end buses differ in the VNX from the CX range?
We have a CX which we are looking to replace with a VNX and the Bus is showing as constantly red on a heat map, what exactly is this showing, how can I measure this bus performance, and how much improved is this in the VNX range. I believe its changed from a FC to SAS bus, is this correct?
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Rainer_EMC
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July 13th, 2012 03:00
Dont forget that while an individual SAS lane is 6Gb the bus (cable) going to the DAE is carrying 4x 6Gb SAS lanes
So it’s a theoretical 6x performance improvement per bus – the typical improvement stated is at least 3x
See http://www.emc.com/collateral/hardware/white-papers/h8217-introduction-vnx-wp.pdf
RRR
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July 13th, 2012 03:00
The 2nd generation CX's use a 2Gb FC bus and the 3rd and 4th generation CX3 and CX4 Clariions use a 4Gb FC bus.
The VNX now has a 6Gb SAS bus, so other than updated processing power, the back end bus is also changed in a not backwards compatible way, such as was the case with CX/CX3/CX4.
If the bus is red on the heat map, this means the bus is overloaded (the max is 400MBps on the CX3/CX4). Are disks overloaded as well? you mentioned the heat map, so why do you want to know how to measure the bus? You're already doing it, right? The tool which produces the heatmap uses NAR files, which you can also use in Analyzer. If you have the licenced Analyzer, you can view the performance live!
You might consider migrating some LUNs to other Raid Groups to spread the load a bit better. Also look at the buses you have: are they loaded equally or do you also have buses that are just slightly used. If all buses and disks are in the red, you need an upgrade to a more powerful system and nowadays that's the VNX. Faster buses, more cpu power, more cache memory.
RRR
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July 13th, 2012 04:00
Indeed, I totally overlooked that fact!
Rainer_EMC
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July 13th, 2012 13:00
When the VNX was first announced I also wondered how going from 4 Gb to 6 Gb gets a 3x+ improvement