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UCS Extended-Memory: what speed?


The Extended-Memory management feature of the UCS C250 servers enables them to configure up to 384 GB RAM on a 2-socket based server. Dell has with the R810 servers that can handle up to 512 GB RAM and has a feature that enables it to use this amount of memory with only 2 of the 4 processors installed, using it's FlexMem Bridge technology (32 banks).

Dell however is very clear about supported memory configurations: it's complex and only certain configurations lead to using the full bandwith of the DDR3 memory modules: up to 64 GB it will run at 1333 MHz, there above at 1066 MHz. The R815 (with AMD proc's) doesn't have the FlexMem Bridge, but will do 258GB at 1333 MHz and 512 at 1066 MHz.

Primary question is: will the UCS C250 M2 run the memory allways at 1333 MHz, no matter how many you put in it? Ofcourse all the same DDR3 modules, spread over the banks as described in the manual.

7 Replies 7

Cisco Employee
Cisco Employee

Yes all slots will run at 1333Mhz assuming

     1. you have a correct Intel CPU that can actually run the memroy at 1333

     2. you have 1333mhz memory

     3. you have a C250 M2 (M1 can only run at 1066 with all dimm slots populated)

So if you put 64GB or 384GB in the box, the memory will run at 1333Mhz. Just make sure to populate one of the recommended C250 memory configurations. Memory will still run at 1333 but you always want to use one of the support memory configurations to get the best peformance out of the box.

I would just make sure that the box as the most recent BIOS and CIMC code to be on the safe side but it should work fine.

Edit: Type change 646GB to 64GB sorry about that. Max memory supported in a B/C250 is 384GB with 8GB DIMMs

Hi Iwatta,

Thanks for the helpfull answer! Then there's this other thing: the supported memory configurations, what are these? When looking for the answer for the speed i searched for the supported memory configurations. I thought that would be the logical step to start from. But even in the manual that isn't mentioned, only very poor information that you shouldn't mix memory types and so on. No numbers or quantities. Can you find me the supported memory configurations for the UCS C250 M2? Perhaps for other readers, it might be helpfull if in this thread you could summarise it too for the C260 and C460.

Regards, Hans

I think i got something, in this case for the M1:

Pages 3-23 and 3-24, state the following possibilities (see pictures attached). Luckily it states something about the M2, saying not all configs are supported on the M2. It suggests that the M2 can not be populated with 4, 8 or 12-dimm configurations. That would suggest that the M2 can be configured with 64GB or more.

Can you please confirm this?

Got a page of a document from Cisco, specific for B250 M2 and C250 M2, please see attachment. Optimized steps are: 48, 96, 192 and 384 GB Ram.

Please take note!

VMware only supports up to 256 GB RAM unless you have the Enterprise Plus-bundle.


Thanks for posting that link - the reminder about memory limitation for vSphere by license used!



As far as supported memory configurations I would consult the Cisco ordering tool. I'm not certain what I have is current so I always tell folks to check the ordering tool as I know it is kept updated.

What you have below are the optimized configs, we can support other memory configs in the server if you need a different memory footprint.


Hi Louis,

Where can i find this "Cisco ordering tool", do you perhaps have a link for me? Nevertheless i find it hard to understand that it's so hard to get to this info.

Edit: what would the best config for 256 MB? And will it perform equally to an optimal 192 GB RAM config (6x 16)?

Kind regards,

Hans Rattink

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