RAM For Server (6x8GB or 12x4GB?)

harvey.l12 · 9 Jan 2017 at 09:38

Hi,

We are looking at getting 48GB of RAM for a server and was wondering if it is better to get 6x8GB or 12x4GB? Are there any benefits for having less RAM modules or more RAM modules at all for performance of the server etc.?

What would be the benefits and draw backs of having only 6 Modules instead of 12 and 12 instead of 6 Modules?

Thanks.

Semple · 9 Jan 2017 at 09:56

How many slots per CPU?

Going on a vague memory, but i'm sure if you fill up all slots, the memory runs at a slightly slower speed than it would do when not running with full slots. Have a look in the manual and see what it mentions about memory configurations.

harvey.l12 · 9 Jan 2017 at 11:28

The server is a Dell R610 with 2x Xeon X5650's with 12 Memory Slots.

We currently have 12 x 2GB UDIMM's and CPUz says it is running in triple channel.
Should we be looking at getting RDIMM or UDIMM?

Is there any performance difference between the UDIMM and RDIMM? I believe i read that UDIMM only supports up to 48GB and RDIMM is up to 192GB... Is this true?

decto · 9 Jan 2017 at 14:23

rdimms are buffered so place a lot less electrical load n the memory interface allowing more modules to be used. Desktop boards typically used unbuffered hence the typical limit of 2 per channel. If you use udimms, you will be able to support a lot less memory.

The world is full of cheap Rdimm ECC memory from thousands of data center servers which is difficult to sell on since it's not compatible with the desktop (in most cases) so likely to be more economic to buy registered if you can buy second hand.

6 or 12 sticks should be fine, ideally a multiple of 6 as you have 3 channels per CPU so to fill each channel you need at least 6.

Personally I'd go for used DDR from a reputable system dismantler, ex server stuff is cheap and plentiful, why stop at 48GB

harvey.l12 · 9 Jan 2017 at 14:40

The manual doesn't show a 16GB memory configuration but should 16GB still be supported by the motherboard?

Also would it be possible to run 4x16GB or 8x8GB (as an example) in dual channel instead of triple channel configuration?

harvey.l12 · 10 Jan 2017 at 16:28

Any Ideas?

#Chri5# · 10 Jan 2017 at 16:34

Out of interest, what OS are you running?

Ricimer · 10 Jan 2017 at 19:51

I would try and stick with full channels, so 6 or 12 only. 16GB sticks may work but it's probably a risk for compatability, it would be safer to stick to 8x6 or 8x12 for 64/128GB

The poweredges are very fussy about memory configurations and will probably complain with 8x4 or 8x8, sometimes it won't even boot with a configuration deemed valid, but not filling a channel.

Edit: For RDIMMs, avoid UDIMMs and you can't mix.

nutcase · 10 Jan 2017 at 20:36

There should be Dell documentation with acceptable combinations. As someone said above filling all the slots usually ends up with a reduction in speed.