Dell R720 and PC3L 12800R memory modules

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Dec 6, 2019

I'm negotiating a purchase of a Dell R720 with the following specs:

Dell R720 SFF with 16x 2.5" bays
2x Intel Xeon E5-2695v2
128Gb RAM
Perc H710 Mini Raid Card

The RAM memory is supposed to be PC3 10600R, but I can change it to PC3L 12800R memories, and I'm trying to understand what are the main differences.

The PC3L means it is an LRDIMM and thus it will not have the rank rule when adding more memory modules?

Or it simply means it is a 1.35v module and still I have to check if it's a single/dual/quad rank module?

The machine will get a proxmox install and will run 2 Windows Server VMs, and a couple of linux hosts for some services (using ZFS with samsung enterprise PM897 SSDs). I believe such machine will be up to the task?

Thank you.
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Sean Ho
Nov 19, 2019
Vancouver, BC
PC3L supports 1.35v. It'll usually default to 1.5v unless set in otherwise in BIOS. 1.35v also means slower speeds. I'd get those if only because they support 12800 at 1.5v. They are still regular RDIMM, not LRDIMM. Up to 8 ranks per channel.

(LRDIMMs are still subject to the rank limitation, just that they present 4 physical ranks as 2 logical ranks (or 8 as 4, etc.). So you could, for instance, fill all 24 slots (3DPC) with 4R LRDIMM, since each channel would only see 6 logical ranks. Can't do that with 4R RDIMM. The downsides of LRDIMM are that they were more expensive (though the gap has closed), and cannot be mixed with RDIMM, and in DDR3 incur a slight latency penalty.)
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