Memory choices for the IBM System x3300 M4

Reverting to 3 memory channels per processor – max at 2 DPC

Thanks to Daniel Bowers for clarifying the use of “socket B” Xeon E5-2400 processors in this server.

IBM has announced the x3300 M4 servers – which are 2-socket servers containing 12 DIMM slots.

The 12 DIMM slots suggest these are running at 3 memory channels per processor (as opposed to the 4 memory channel Romley processors seen so far on this blog). And maximum memory capacity is at 2 DPC.

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Running at 3 memory channels per processor ?

The IBM x3300 M4 server – which is a 2-socket server – seems to have 12 DIMM slots according to the spec sheet:

http://www-03.ibm.com/systems/x/hardware/tower/x3300m4/index.html
http://public.dhe.ibm.com/common/ssi/ecm/en/xsd03148usen/XSD03148USEN.PDF
IBM System x3300 M4

Memory (max) Up to 192 GB*, 12 slots (UDIMM/RDIMM)

*32 GB LRDIMMS will be available in the first half of 2013 for
a maximum capacity of 384 GB.

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Back to 3 memory channels per processor

12 DIMM slots would suggest 6 DIMM slots per processor – which would suggest 3 memory channels (as opposed to the 4 memory channels for Romley ?):

2 processors x 3 memory channels per processor x 2 DIMMs per channel (DPC) = 12 DIMM slots

The reason these have 3 memory channels (like the pre-Romley servers) – and different from the 4 memory channels on most Romley servers is because these are “socket B” Xeon E5-2400 processors (3 memory channels) – as opposed to “socket R” E5-2600 processors (which have 4 memory channels) (thanks to Daniel Bowers for clarifying this).

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Availability of 32GB LRDIMMs

It is interesting that 32GB LRDIMMs are not listed in the memory options – and only as a footnote pointing to 32GB LRDIMM availability in Q1 2013.

The reason may be that 32GB LRDIMMs qualification may not have completed on this server yet and may complete by Q1 2013 as IBM suggests.

IBM makes no mention of HCDIMMs – if they are being qualified for this server, IBM is not pre-publicizing it as it is doing for LRDIMMs.

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Memory choices

Using 16GB memory modules, the best option would be 16GB RDIMMs (2-rank) for a maximum of 192GB per server.

As outlined earlier:

https://ddr3memory.wordpress.com/2012/06/29/infographic-memory-buying-guide-for-romley-2-socket-servers/
Infographic – memory buying guide for Romley 2-socket servers
June 29, 2012

Using 32GB, the 32GB RDIMMs (4-rank) will not perform well as examined here:

https://ddr3memory.wordpress.com/2012/06/20/non-viability-of-32gb-rdimms/
Non-viability of 32GB RDIMMs
June 20, 2012

So the 32GB LRDIMMs or 32GB HCDIMMs would have to be used.

Of these, the 32GB HCDIMM will outperform the 32GB LRDIMMs:

https://ddr3memory.wordpress.com/2012/07/27/awaiting-32gb-hcdimms/
Awaiting 32GB HCDIMMs
July 27, 2012

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Conclusion

The above set of constraints point to these choices for maximum memory:

– 16GB RDIMM (2-rank) at 2 DPC – for a maximum of 192GB
– 32GB HCDIMM at 2 DPC – for a maximum of 384GB

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