rack-scale flash

Rack-scale flash is flash-only storage that uses a high-speed interface to connect the storage more directly to the CPU than with a traditional storage array. The most common connection is nonvolatile memory express (NVMe) connected via a network fabric. This interface is called NVMe over Fabrics (NVMe-oF).

Rack-scale flash is also known as shared flash storage because it creates a pool of storage that is shared by servers over the high-speed interconnect inside one or more racks. Others call the concept of sharing compute, storage and networking as resource pools composable infrastructure.

By using the NVMe protocol, rack-scale flash vendors can deliver much lower latency while keeping the same throughput levels available from network transports such as 32 gigabit Fibre Channel (FC) or 40/50/100 Gigabit Ethernet (GbE). The lower latency improves the IOPS of the overall system, making rack-scale flash best suited for high-performance computing needs. Examples include artificial intelligence, real-time analytics of big data and in-memory database systems.

Rack-scale flash vendors

There are two main types of rack-scale flash suppliers: those that use off-the-shelf solid-state drives (SSDs) and those that use custom flash modules. The former are generally startups such as Apeiron Data Systems, E8 Storage, Excelero and Mangstor. The latter are rack-scale flash vendors such as tech giants IBM and Hitachi Vantara.

Two early startups are Pure Storage, founded in 2009, and DSSD Inc., founded in 2010. Pure began life as a flash-only storage provider and entered the rack-scale flash market in 2016 with its FlashBlade product.

DSSD, in comparison, was acquired by EMC Corp. in 2014 for its rack-scale technology. In 2016, the newly merged Dell EMC launched DSSD D5, a rack-scale flash appliance based on the acquired technology. The company cancelled the line in March 2017, stating it made more sense to embed the technology into existing storage arrays.

Benefits/drawbacks of rack-scale flash

Rack-scale flash boosts the performance of any system, even more than all-flash arrays that don't connect via low-latency NVMe protocols. All-flash array vendors claim IOPS ranging from 200,000 to the low millions. Dell EMC, for example, claimed 10 million IOPS for its now cancelled DSSD D5 product. While any application can benefit from that speed, it is a necessary feature for financial applications, big data technology such as Hadoop, and in-memory database systems such as SAP HANA.

Eric Chang, program manager at
SK Telecom, explains the firm's
NV-Array for rack-scale storage.

The primary drawback of rack-scale flash is related to cost. Not only is it an all-flash array system, most rack-scale flash vendors use the NVMe-oF protocol, which is still an early stage technology compared to SCSI or TCP/IP. However Apeiron uses NVMe over Ethernet, instead of a fabric such as InfiniBand or FC. The vendor claims 18.4 million IOPS for its product.

Another drawback related to cost is the sheer amount of flash used in rack-scale flash, which has a very high storage density in relation to a standard all-flash array. For example, the Dell EMC DSSD D5 could have up to 36 flash modules for a total of 144 TB of raw flash storage, in a 5U appliance.

This was last updated in December 2017

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