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Kioxia releases PCIe 5.0 EDSFF SSDs

Kioxia became the first vendor to release a PCIe Gen 5.0 SSD with its new CD7 series. Still, it highlighted the EDSFF specification over beating the Gen 5 drum.

Kioxia launched the CD7 SSD series and became the first vendor to offer a drive using PCIe 5.0 interface, which doubles the performance over PCIe 4.0 from 16 gigatransfers per second to 32 GTps. The new SSD series utilizes the Enterprise and Data Center SSD Form Factor, on which the vendor also announced general availability for its XD6 SSDs.

The new SSDs are based on Kioxia's fourth-generation BiCS Flash 3D NAND technology, proprietary controller and firmware. The CD7 Series supports four PCIe lanes but is optimized for PCIe Gen 5.0 x2, saving two lanes for connections to other PCIe devices such as GPUs or field-programmable gate arrays, according to a press release. The vendor claims speeds as high as 6,450 MBps and over 1 million IOPS for read with latency as low as 75μs read and 14μs write.

Vendors, especially in data centers, are using more flash in the form of SSDs for primary storage, said Tom Coughlin, president of Coughlin Associates. 

"Data is mainly stored in colder storage," Coughlin said. "However, operational data is on faster storage such as NVMe SSDs, and there is a real growth opportunity there in the market."

Currently, PCIe 4.0 is the dominant interface in the NVMe SSD market. But PCIe 5.0, which debuted in May 2019, will likely become the dominant interface in the next couple of years, and vendors like Kioxia that prepare for that transition early will be in a good position once PCIe 5.0 becomes the leader, he said.

Early start on PCIe 5.0

Kioxia may be the first major vendor with a PCIe 5.0 drive, but it's not beating its chest around the new interface. It supports the Gen 5 interface, but it is optimized for PCIe 4.0 x4, according to Ilya Cherkasov, senior product manager of the enterprise SSD division at Kioxia.

Kioxia CD7 PCIe Gen5 EDSFF E3.S SSD
Kioxia CD7 PCIe Gen5 EDSFF E3.S SSD

"We are more focused on Gen 4.0 x4 saturation now than what Gen 5.0 might do," Cherkasov said.

Kioxia's CD7 is the first Gen 5 SSD announced, releasing it to compete alongside the current Gen 4 market, he said. Gen 4 drives provide more than enough performance for most current enterprise applications, Cherkasov said, but when Gen 5 becomes necessary and support begins, Kioxia will be ahead of the competition.

During a demonstration at the recent Open Compute Project, Kioxia showed the drive performing around its claimed numbers, which was in line with high-end Gen 4.0 SSDs. Cherkasov said the CD7 can go up to 180,000 write IOPS in order to meet the modern demand of the data center.

Kioxia was one of the first major vendors to release a PCIe 4.0 SSD. Being first to market allows competitors to see what Kioxia did and respond, he said. The CD7 Series builds on late Gen 4.0 entrant's products while preparing itself for the Gen 5.0 market.

Architecture tweaks and form factor

The CD7 Series is Kioxia's data center drive, meaning the SSDs are more general purpose and aren't built specifically for the highest-end enterprise use cases. The CD7 Series comes with enterprise-grade features such as die failure protection and reliability, Cherkasov said.

The CD7 Series also includes the Enterprise and Data Center SSD Form Factor (EDSFF) E3.S 7.5 mm, which is roughly the same size as and a replacement for 2.5-inch drives. The drive comes in capacities of 1.92 TB, 3.84 TB and 7.68 TB. Kioxia said the E3.S allows for more density in the same footprint.

EDSFF and connector benefits

The EDSFF specification offers benefits beyond new form factors as well, Cherkasov said. The connector may be a key to better utilizing PCIe technology as it moves toward higher performances.

The connection offered by EDSFF is more robust in terms of signal integrity compared with the SFF-8639 currently used for NVMe connections in the enterprise. The pinout to SFF-8639 connectors used in U.2 and U.3 drives are already presenting challenges when trying to use the full speed of PCIe 5.0, he said. If PCIe 6.0 doubles the signal frequencies once more, Cherkasov said it's questionable that the SFF-8639 will be able to manage the additional frequencies between the CPU and the drive, but the EDSFF connector can.

The new connector on EDSFF is designed to support PCIe 5.0 and PCIe 6.0 architectures, according to a blog post by Mike Scriber, senior director of server solution management at Supermicro.

The connector also allows for more power -- up to 40 watts -- thus potentially more performance and better cooling.

SSDs don't have to be as rigid with its design as HDDs, Coughlin said. There are no disks or heads to move around, which allows for more flexibility in form factors while still fitting in the standard rack sizes. Through the work of Open Compute Project and SNIA, EDSFF is becoming the standard.

XD6 SSD hits GA

Kioxia also announced the general availability of Kioxia XD6, a PCIe 4 data center drive that also uses EDSFF. The XD6 uses E1.S SSDs and benefits from the new connector, according to Peter Gamboa, data center SSD product manager at Kioxia.

Kioxia XD6 EDSFF E1.S SSD
Kioxia XD6 9.5mm EDSFF E1.S SSD

The dimensions on the XD6 are like an M.2 drive and can be seen as an M.2 replacement in the data center, Gamboa said.

The E1.S has better thermal support, hot-plug capability and higher capacity in the footprint. M.2 is limited to roughly 4 TB per drive, whereas the E1.S XD6 can go up to 8 TB, although customer demand for the higher capacity is not there yet, he said.

The XD6 is offered in three Z-heights: 9.5mm, 15mm and 25mm, with a higher capacity on the latter two. The most significant difference between the 15mm and the 25mm is the size of the heat sink, with the 25mm having almost twice the heat sink as the 15mm. This could potentially lower the amount of density in a given rackspace. While Gamboa said the 9.5mm may be the sweet spot in terms of storage and cooling, some data center customers such as those that run high-performance computing applications still look at the much thicker 25mm version for its larger heat sink.

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