As promised in my previous post, lets go through the blades available in Ciscos Unified Computing System. Essentially we have a few flavours of blades, full width and half width blades, some which utilise extended memory architecture (co developed by Intel and Cisco, which we’ll touch on), Daul socket for the most part with the exception of one which is 4 socket and a veritable feast of different memory options, processor options, IO card options and drive options.
However, I wanted to start with the component pieces before we delve into schematics (because you can read about those on the Cisco Site) and spend a little more time on each piece.
So what is this extended memory architecture Cisco keep bangin on about ? lets start with the why before we get to the how. Any tom, dick and harry can stick a load of Memory DIMMs in a server and scream about the fact they’ve got a few hundred gig of memory.. so why is this different ?
Typcally each CPU on a server has 3 memory channels for… you guessed it.. accessing memory. The number of transfers per second at which memory will perform is typically dictated by the number of DIMMs that are populated per memory channel. Typically when you populate 1 x DIMM per memory channel memory runs at 1333 MTpS (Million transfers per second), when you populate 2 DIMMs it would run at 1066 MTpS and when you get to a depth of 3 DIMMs per channel you’re running at 800 MTpS (not ideal). So as memory desity gets higher, performance can suffer (as shown below).
Cisco, in combination with Intel have developed something called the Catalina chipset. Despite sounding like a car, the Catalina chipset is quite a nifty addition. Effectively acting like a RAID controller for memory, it sits downstream of the CPU memory controllers (one per memory channel) and presents out four additional memory sockets per channel, then presents an aggregate of the memory sitting beneath it as one logical DIMM up to the CPU memory channel, meaning that you can have denser memory configurations without memory ever clocking in below 1066 MTpS ( as shown below).
The two benefits of this being that you can address a larger amount of memory for memory intensive applications/virtual machines/whatever with a lower socket count, also making it possible to see higher consolidation ratio’s when virtualising machines or you can achieve moderate memory configurations using lower capacity less costly DIMMs. Cisco currently utilise this technology with the Westmere and Nehalem CPUs, B250 Blades servers and C250 Rackmount servers.
I nice little clip from the Cisco Datacenter youtube channel with a brief intro into extended memory
Either way.. not a bad idea..