CXL 2: Pooling, sharing, and I/O-memory resources [LWN.net]

CXL 2: Pooling, sharing, and I/O-memory resources

Posted May 21, 2022 3:38 UTC (Sat) by willy (subscriber, #9762)
In reply to: CXL 2: Pooling, sharing, and I/O-memory resources by Cyberax
Parent article: CXL 2: Pooling, sharing, and I/O-memory resources

As opposed to a 32GB DIMM for $560?

https://www.insight.com/en_US/shop/product/P00924-B21/HEW...

It's not "vaporware" just because you don't want to pay for it. And you can buy an Exadata X9M with 18TB of PMem per rack (admittedly that's spread over three servers each with 6TB). I did think we'd have more capacity by now (about double what we have). But an undershoot on capacity is hardly the same thing as "doesn't exist". It was always going to be a high-end option.

CXL 2: Pooling, sharing, and I/O-memory resources

Posted May 21, 2022 6:53 UTC (Sat) by Cyberax (✭ supporter ✭, #52523) [Link] (2 responses)

You can buy them much cheaper: https://memory.net/product/m393aag40m32-cae-samsung-1x-12...

But yep, this means that the persistent RAM is pretty much a non-entity now. It needs special chipsets, it's expensive, it's not available through most cloud computing providers.

CXL will likely be similar once people find out that it's nowhere close in speed to normal RAM.

CXL 2: Pooling, sharing, and I/O-memory resources

Posted May 21, 2022 11:58 UTC (Sat) by willy (subscriber, #9762) [Link] (1 responses)

I was comparing apples-to-apples. PMem from this vendor vs DRAM from this vendor. PMem is cheaper per bit than DRAM, just as promised. It's more expensive per bit than NAND, also as promised. It's available in large capacities, so the price of a DIMM is high.

If you were expecting it in your laptop by now, then you weren't paying attention. You also don't have 100Gbps networking in your laptop, but it very much exists.

I think I'm done here. You said something stupid and hyperbolic; now you're determined to Be Right. It doesn't really matter what the facts are.

CXL 2: Pooling, sharing, and I/O-memory resources

Posted May 21, 2022 18:56 UTC (Sat) by Cyberax (✭ supporter ✭, #52523) [Link]

> PMem is cheaper per bit than DRAM

Except that it's not. At best it's about the same, and certainly machines with tens of terabytes of NVRAM are in the realm of exoticware for at least a decade more. This situation is far away from the hyped state where NVRAM was going to be ubiquitous.

> You also don't have 100Gbps networking in your laptop, but it very much exists.

I have 40Gbps networking at home, and it's not even that expensive. It's not in my laptop (for some reason adapters max out at 10GBps), but I certainly can use it otherwise.