Intel Optane PMem

Capacity per socket: the Cascade Lake memory limit

On 2nd Gen Xeon Scalable, PMem counts towards the CPU's maximum memory. Standard models address 1 TB per socket, M models 2 TB and L models 4.5 TB. With six PMem modules and six 32 GB RDIMMs per CPU, that gives:

• 6 × 128 GB PMem + 192 GB DRAM = 960 GB: works with any supported CPU, including the Gold 6248R.
• 6 × 256 GB PMem + 192 GB DRAM ≈ 1.7 TB: needs an M or L CPU.
• 6 × 512 GB PMem + 192 GB DRAM ≈ 3.2 TB: only possible with an L CPU.

In practice the 128 GB module is therefore the most common choice: it doubles to quadruples memory per socket without forcing a more expensive CPU variant. DRAM modules for the same channels are listed under DDR4 ECC RAM.

When persistent memory pays off – and when it doesn't

• Many VMs or VDI desktops: in Memory Mode, main memory grows without any software changes. Ideal when VMs reserve a lot of memory but actively use only part of it.
• SAP HANA and PMem-aware databases: in App Direct mode, data survives a reboot, so large datasets are back in memory much faster.
• Less suitable: applications that constantly access the whole memory at random, any AMD system, and new purchases on current platforms.

You set the mode in the BIOS or, on Linux and Windows, with Intel's ipmctl tool. Decide before going live: switching between Memory Mode and App Direct later rebuilds the memory regions, and anything stored in the persistent area is lost.

Don't confuse the PMem modules with the Optane SSD DC P4800X, an NVMe SSD built on the same storage medium, which you'll find under server SSDs.