NVMe RAID
Overview
End users continue to rely on RAID for server level primary storage protection. Crucial applications of RAID include cost-effective protection from drive failure for boot volumes, primary data storage and database applications.
Previously, NVMe device use has been confined to high-performance applications, due to their high cost. But, as these costs have started to subside, the ability of the Enterprise to adopt NVMe drives for traditional use models have emerged. Today NVMe SSD volumes are fast becoming the preferred storage media for capacities <4TB, according to IDC. In addition, other ecosystem barriers for NVMe primary storage have also been removed: |
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- Enterprise reliability (write endurance)
- Serviceability (hot plug, surprise plug)
- Standardization (Universal Bay Management)
- Technology for ubiquitous connectivity of SAS/SATA/NVMe (Tri-mode)
The removal of ecosystem barriers and the rising popularity of NVMe drives in the Enterprise server space means that RAID for NVMe SSDs will be a mandatory portfolio offering for enterprise servers by the end of the decade.
Options for RAID in NVMe Ecosystems
As seen with option 1, software RAID utilizes the in-box NVMe device driver on the host to access NVMe drives directly or via a switch where necessary. Utilizing the inbox driver provides the lowest possible latency path from the host to the drives, and superior i/o performances when compared to traditional hardware RAID. A detriment of software RAID is the consumption of expensive compute and memory bandwidth on the host.
In option 2, single path hardware RAID relieves the parity generation burden from the host. The use of single path hardware RAID funnels all data to the RAID controller hardware prior to placing them on the submission queue of the drive. Directing all data through the RAID controller, adds latency for read/write operations, even with intelligent bypass options are available to reduce unnecessary steps for various traffic patterns.
Option 1 - Software RAID Architecture | Option 2 - Single Path RAID Architecture |
Option 3 combining a multi-path driver with an embedded switch in the controller unlocks the best of both worlds for PCIe attached drives. The embedded switch provides a streamlined data path through the adapter unencumbered by firmware nor the raid on chip controller, all while maintaining the availability of hardware based advanced data services. The novel embodiment of the architecture is the multi-path driver which intelligently manage data based on the data service requirements through either the switch or the controller with negligible overhead.
Option 3 - Multi Path RAID Architecture
Multi-Path Drivers and the Path to Standardized Drivers
NVMe SSDs offer high IOP and low latency performance which need to be preserved when utilizing data protection services such as RAID. Traditional data protection has relied on either a software solution which consumes valuable CPU resources or a single data path RAID controller with larger than optimal latency values. As the next generation of flash media drives emerges, redesigning traditional data protection architectures is required.
Multi-Path Driver Operation |
All interactions with the multi-path driver present NVMe SSDs as SCSI devices. A standardized driver would interface directly to NVMe drives via the PCIe switch when offloading is not required; or it could interface to a storage controller that presents itself as a logical NVMe drive that's attached to the switch.
Conclusion
NVMe SSDs offer high IOP and low latency performance which need to be preserved when utilizing data protection services such as RAID. Traditional data protection has relied on either a software solution which consumes valuable CPU resources or a single data path RAID controller with larger-than-optimal latency values. As the next generation of flash media drives emerges, redesigning traditional data protection architectures will become a significant undertaking.
Microsemi RAID adapters and controllers (ROCs) supporting NVMe architecture will sample soon.