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Marvell PFMA: Optical Memory Fabric for AI KV Cache Bottlenecks

Converge Digest USA
Overview
Marvell has introduced the Photonic Fabric Memory Appliance (PFMA), a rack-mountable system designed to share 16–32 TB of DDR5 memory across up to 16 servers via optical links. By treating memory as a cluster-wide resource, the architecture aims to increase concurrent conversations by approximately six times compared to traditional configurations.
In Depth

Key Findings

Marvell is targeting the key-value (KV) cache bottleneck in AI inference to prevent redundant computations during long conversations in reasoning models and agentic applications. Simulation-based analysis indicates that a shared-memory configuration can support approximately six times as many concurrent conversations at a comparable time-to-first-token using the same compute resources. These results are based on workload-specific modeling and pre-silicon estimates.

Technical Details

The PFMA is a rack-mountable appliance featuring 128 standard DDR5 DIMM slots and approximately 1 TB of HBM3e, which functions as a cache for the larger DDR5 pool. The system utilizes sixteen Photonic Fabric Memory Modules connected through a passive fiber shuffle to create a unified shared address space. Marvell provides two integration options:

  • PF-NIC card: Uses PCIe Gen6 x16/CXL 3.x for server connectivity.
  • PF-Chiplet: Integrated directly into an XPU package.

The practical optical reach for memory sharing across racks is identified as 25–30 meters to balance physical separation against propagation delay. Marvell positions the chiplet-attached PFMA as a G1.5 tier below local GPU HBM, while the server-attached version serves as a G2.5 tier between system DRAM and storage.

Background & Context

The technology, acquired through Celestial AI in February 2026, expands Marvell’s memory strategy beyond Bravera storage controllers and Structera CXL expansion. The goal is to keep reusable KV cache closer to compute than SSD-based offloading, allowing inference software to flexibly assign workloads to different processors without repeating prefill work.

Significance & Outlook

This architecture shifts KV cache placement from a local component to a cluster architecture decision. However, realized performance remains dependent on cache hit rates, DDR bandwidth, fiber length, and the ability of serving software to manage compatible cache entries. The PFMA represents a move toward treating memory as a shared cluster resource rather than a standalone server component.

Source: https://convergedigest.com/pecc-summit-marvell-optical-memory-kv-cache/

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