Mixing DIMMs in servers

chuckk281 — Wed, 18 Sep 2013 21:24:24 GMT

Customer question for Tarek that he needed some assistance:

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My customer was trying to mix DIMMs with different voltage, when he did this test the server started randomly.

He used the following parts :

HP 4GB (1 x 4GB) Single Rank x4 PC3L-10600R (DDR3-1333) Registered CAS-9 Low Voltage Memory Kit	647893-B21
HP 4GB (1 x 4GB) Single Rank x4 PC3-12800R (DDR3-1600) Registered CAS-11 Memory Kit	647895-B21

Is that configuration supported ?

If no, do we have any documentation ?

Thank you in advance for your help.

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Reply from Eirik:

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Seems supported. The 1.35v DIMMs will be operating at 1.5v. Do check the rules for your particular model of server.

E.g. the DL380pGen8 Quickspecs mention :

General Memory Population Rules and Guidelines:

White DIMM slots denote the first slot of a channel. For 1 DPC (DIMM per channel) populate white slots only.
Install DIMMs only if the corresponding processor is installed.
If only one processor is installed in a two processor system, only half of the DIMM slots are available.
To maximize performance, it is recommended to balance the total memory capacity between all installed processors and to load the channels similarly whenever possible.
Populate DIMMs from heaviest load (quad-rank) to lightest load (single-rank) within a channel. Heaviest load (DIMM with most ranks) within a channel goes furthest from the processor
RDIMMs operating at either 1.35V or 1.5V may be mixed in any order, but the system will power them at the higher voltage.
Do not mix RDIMMs, LRDIMMs, and UDIMMs.
LRDIMMs are supported up to 3 DIMMs per channel.
Using the HP RBSU, 1.35V DIMMs can be changed to operate at 1.5V.
DIMMs of different speeds may be mixed in any order; the server will select a common optimal speed.
The maximum memory speed is a function of the memory type, memory configuration, and processor model.
The maximum memory capacity is a function of the memory type and number of installed processors.
HP memory from previous generation servers is not qualified on the DL380p Gen8 Server. Certain HP SmartMemory features such as memory authentication and enhanced performance may not be supported.
To realize the performance memory capabilities listed in this document, HP SmartMemory is required. For additional information, please see the HP SmartMemory QuickSpecs at: http://h18000.www1.hp.com/products/quickspecs/14225_div/14225_div.html.

For memory population rules and additional memory guidelines, please see the DL380p Gen8 user guide at http://www.hp.com/support.

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Mixing DIMMs in servers