PCIe connectivity has gained an increased profile in enterprise data storage in recent years, in particular with the emergence and takeover of mainstream flash storage by NVMe-based hardware.
For decades, data storage connectivity centred on SCSI-based protocols (eg, SAS and SATA). And when NVMe flash came along, with I/O potentially boosted by orders of magnitude compared to existing SSDs, it too was often connected via “traditional” interfaces in storage products.
That has recently begun to change with the emergence of EDSFF – or Enterprise and Data Centre Standard Form Factor – dedicated to marrying NVMe flash with PCIe connectivity, and specifically PCIe 4.0 onwards.
Here we will look at PCIe generations 4 and 5 and look forward to gen 6, with a particular eye on their use in enterprise storage.
PCIe generations: 4, 5, and 6
PCIe revisions generally spend a few years going from inception to productisation and require broad ecosystem support, such as in CPUs, to support storage products properly.
PCIe 4.0 – or gen 4 – was, for example, first announced in 2011, but is currently the newest PCIe connect with more than token product availability.
Gen 4 has a link speed of 16 gigatransfers per second (Gtps), which can be up 64GBps depending on the number of lanes.
Each PCIe generation doubles the performance of the last, so gen 5 delivers 32Gtps or a potential 128GBps bandwidth. There are some products, but not many.
Work on PCIe gen 6 was announced in 2019, with products some years away.
Gen 4 hitting mainstream now
Gen 4-equipped flash drives with capacities as high as 30TB-plus were available by late 2020 from Intel, Kioxia, Samsung and Micron.
Intel joined AMD in supplying Ice Lake CPUs that supported PCIe 4.0 in 2021
More recently, EDSFF form factor drives have become available from Intel, Kioxia and Samsung, with PCIe 4.0 connectivity available and TLC and QLC flash media on board.
Among the big five storage product makers, PCIe gen 4 is just about arriving in arrays, and where it hasn’t arrived, they’ve got it in some server products (if they supply them).
Dell EMC offers PCIE gen 4 drives in PowerEdge servers (with Intel Ice Lake CPUs), while
IBM offers PCIe 4.0 drives for its Power9 server family.
NetApp announced its AFF A900 high-end all-flash array controllers would be PCIe 4.0-compatible in December 2021.
Pure Storage beefed up the high end of it FlashArray family with the //XL series, which based its upgrade on PCIe gen 4 and Intel Ice Lake CPUs.
Hitachi appears to support Ice Lake in some DS servers, but makes no very public play of PCIe gen 4.
Gen 5: Mostly teasers for now
Gen 5 drives are available from Samsung, with its PM1743, which was announced in December 2021, with a claimed 1.3GBps read speed throughput and random 2.5 million IOPS. That’s nearly double the performance numbers of Samsung’s PCIe 4.0 drives. It will come in capacities of 1.92TB to 15.36TB with mass production this year and will be in 2.5” M.2 or EDSFF form factors.
Taiwanese fabless chip maker Adata has also teased PCIe 5.0 drives, with capacities up to 8TB.
Broad ecosystem support is likely to be an issue for some time, however, with CPU support for PCIe 5.0 from Intel, for example, currently restricted to PCIE slots and not M.2.
PCIe gen 6 got to its final draft specification in late 2021. Products are likely to be available by around 2025 or 2026.
