Hyperscalers Are Racing to Recycle DDR4: The CXL Revolution is Here
The server landscape is on the cusp of a significant shift, and it’s not just about faster processors or more cores. It’s about how memory is accessed, expanded, and shared. At this year’s Future of Memory and Storage (formerly Flash Memory Summit), one thing was abundantly clear: **CXL** (Compute Express Link) is moving beyond hype and into tangible deployments, driven by a surprisingly pragmatic need – extending the life of existing infrastructure.
From Interconnect Standard to Infrastructure Game-Changer
CXL began as a host-to-device interconnect, quickly absorbing competing standards like OpenCAPI and Gen-Z. Built on the familiar PCIe bus, it’s evolved into a versatile protocol capable of addressing a wide range of use cases. The CXL consortium, boasting industry giants like AMD and Intel alongside a vibrant ecosystem of startups, is actively shaping this evolution. At FMS 2024, CXL wasn’t just present; it was a focal point of demonstrations from numerous vendors, signaling a clear acceleration in adoption.
The Rise of Memory Expansion and the DDR5/DDR4 Divide
The transition from DDR4 to DDR5, coupled with the increasing demand for large RAM capacities – particularly in workloads less sensitive to latency – has created a sweet spot for CXL. Memory expansion modules are emerging as the first widely available CXL devices. Samsung and Micron have already announced products in this space, but the innovations showcased at FMS 2024 reveal a maturing market.
SK hynix: Simplifying CXL with CMM-DDR5 and HMSDK
SK hynix unveiled their CMM-DDR5 CXL memory module, offering 128GB of capacity in the standard SDFF (E3.S 2T) form factor. Crucially, they’re addressing the complexity of CXL adoption with the Heterogeneous Memory Software Development Kit (HMSDK). This toolkit, operating at both kernel and user levels, intelligently manages data placement between server DRAM and CXL devices based on usage frequency, streamlining the integration process. SK hynix is also pioneering memory pooling with “Niagara 2.0,” enabling multiple CXL memories to be shared across CPUs and GPUs, a significant step beyond simple capacity sharing.
Micron and Microchip: Reliability and Compatibility with CZ120
Micron, in collaboration with Microchip, demonstrated their CZ120 CXL Memory Expansion Module, built on the Microchip SMC 2000 series controller. A key focus is reliability, with the SMC 2000 incorporating DRAM die failure handling, ECC support, and comprehensive diagnostics. Importantly, the controller’s flexibility allows CXL modules to complement existing DDR5 DRAM, offering a path for incremental upgrades without wholesale server replacements.
Marvell’s Structera: Compute Acceleration and DDR4 Recycling
While many CXL solutions focus on memory expansion, Marvell’s Structera line takes a different tack. Announced shortly before FMS 2024, Structera integrates a compute accelerator alongside memory expansion capabilities. Built on TSMC’s 5nm process, the Structera A 2504 boasts 16 Arm Neoverse V2 cores, four DDR5-6400 channels, and in-line compression/decompression. This combination scales both memory bandwidth and compute power, making it ideal for demanding workloads like Deep-Learning Recommendation Models (DLRM) – and potentially reducing energy consumption.
The DDR4 Lifeline: Structera X Expanders
Perhaps the most compelling aspect of the Structera line is the X 2404 and X 2504 expanders. These devices allow hyperscalers to repurpose existing DDR4 DIMMs – up to 6TB per expander – while increasing overall server memory capacity. The X 2404, consuming a mere 30W, offers in-line compression, encryption, and secure boot. Marvell’s focus on maximizing DRAM capacity (3 DIMMs per channel) and minimizing power consumption underscores their strategy of targeting high-volume customers with practical solutions. As Marvell themselves noted, hyperscalers are eager to get their hands on these expanders.
Beyond the Hype: A Realistic Timeline for CXL Adoption
While the potential of CXL is undeniable, the industry acknowledges that widespread adoption is still some time away. The “hockey stick” growth curve hasn’t arrived yet. However, as more host systems with CXL support come online, the value proposition of solutions like Marvell’s Structera line will become increasingly clear. The initial driver isn’t necessarily bleeding-edge performance, but rather a pragmatic need to optimize existing infrastructure and extend its lifespan. The CXL Consortium continues to refine the specifications, paving the way for broader compatibility and innovation.
What will be the killer app for CXL beyond memory expansion? Will compute acceleration become the dominant use case, or will we see entirely new applications emerge? Share your predictions in the comments below!
