LRDIMM vs RDIMM --- also DUAL vs QUAD RANKing

[benny_r_t_2]

NOTE:  This is for my homelab esxi build to run my Oracle apps and database guest VMs.  I have another thread going in the plan build section of the forums if interested in photos/etc of how that is going.

 

 

Hi,

I need some help understanding my memory purchase options.

Unfortunately I never understood the channel bandwidth rules very well. I understand to purchase in matching pairs, but I never understood if that meant having to match throughout on all channels. On top of my confusion there, I'm reading about RDIMM vs LRDIMM and dual RANK vs quad RANK.

I'm tending to lean toward higher density sticks.

First, here is layout of my board and the quick reference for memory pairing:

Initially I would like to purchasing 128GB RAM.

My options, I think, are:

four sticks of RDIMM 32GB dual rank

or

two sticks of LRDIMM 64GB quad rank


pricing for the 128GB is pretty close using either solution.

Could my decision on #"rank" limit me in some way later down the road?

Sorry for my confusion. In short, I would like to initially purchase two LRDIMM 64GB sticks unless I'm shooting myself in the foot with LRDIMM quad RANK (some limitation maybe I'm not aware of?), in which case I'll go with four 32GB dual rank RDIMMs.  If I eventually max out the 6 channels with 32GB each that is still a hefty 192GB per CPU.  But if I can I would like to have higher density 64GB sticks, but not if that has some issue I'm unaware of. 

Thanks!

Benny

[benny_r_t_2]

Update:

Although i still don't fully understand lrdimm vs rdimm or RANKs i decided on 32GB sticks. My logic is that when i eventually do purchase a2nd cpu, with 32GB sticks instead of 64GB sticks I'll have more sticks to move over to from cpu1 to cpu2. And honestly 192GB via 6 channels per cpu ain't bad at all.