Data storage is an increasingly important component of many OpenVPX (VITA 65) systems. Intelligence, Surveillance, and Reconnaissance (ISR) systems, for example, generate large volumes of data that must be recorded in real time for later analysis. These systems require high capacity and performance, often combined with strict Size, Weight, and Power (SWaP) constraints.
Storage implementations used with these systems have historically fallen into two categories: 1) low-capacity, low-performance embedded storage boards, or 2) higher-capacity, higher-performance but physically larger and heavier external storage boxes or subsystems. However, current flash-based Solid-State Drive (SSD) technology, combined with optimized storage controller architectures, has fueled the development of embedded storage blades that provide very high levels of consistent performance, reliability, and capacity.
This new generation of storage blades enables fully embedded blade-level storage that yields the same (or better) performance and capacity as large external storage boxes, but combined with ultra low SWaP. A single slot 6U OpenVPX embedded storage blade can now offer greater than 600 MBps of sustained read/write performance, a capacity of more than 3 TB, and power consumption of less than 30 W. This blade-level solution can be contrasted with external RAID or NAS boxes that may consume hundreds of watts and weigh 50 or more pounds.
OpenVPX connection supports many storage models
The rich backplane I/O capabilities provided in OpenVPX systems (particularly as compared to VME or VXS) allow embedded storage blades to support a wide variety of host interfaces, protocols, and storage models. Storage interface options often used in OpenVPX include 1/10 GbE, Fibre Channel, backplane PCIe, and others. Typical storage models include: Direct Attached Storage (for block-level data access, or RAID); Network Attached Storage (for file sharing) using NFS, FTP, CIFS/SMB, and other protocols; and high-performance data recording modes. The underlying storage controller may provide support for both RAID0 (highest performance) as well as RAID5 (redundant data protection).
As a primary or secondary OpenVPX board-to-board interconnect, PCIe and 1/10 GbE provide an efficient interface to embedded storage blades. A four-lane “Gen 1” PCIe backplane interface provides about 2 GBps aggregate storage access bandwidth, while newer “Gen 2” interfaces provide twice that. Backplane 1/10 GbE provides an efficient (but lower performance) method for hosts to access storage blades in a file sharing or NAS mode, as well as providing RAID/DAS access using iSCSI or Fibre Channel over Ethernet (FCoE).
High-performance RAID enabled by next-gen SSDs
Flash-based SSDs are the foundation of the new generation of OpenVPX embedded storage blades. While flash SSDs have been available for years, early versions were unsuitable for high-performance embedded usage, hampered by low capacity and poor (and highly inconsistent) performance. SSDs are still not all created equal, and thus it is critical to match SSD characteristics to the end application.
Three key performance metrics for SSDs in OpenVPX and other systems are: 1) sequential write performance (measured in MBps); 2) random write performance (measured in IO/s); and 3) what is perhaps the most important for real-time systems: consistency in performance. The first two characteristics are easy to measure, but the third is not. Nearly all SSDs suffer from a significant “memory” effect, where previous usage (and access patterns) can dramatically affect future performance. A “fresh” SSD might write sequential data at 200 MBps (sustained). But that same SSD, after having been exposed to a write-intensive access pattern for only a short time, might only be able to write data at 50 MBps.
Advancing VITA 65 systems with SSD-based blades
Storage blade and controller architectures that leverage the strengths of new-generation SSDs (and compensate for their shortcomings) result in powerful and compelling blade-level OpenVPX storage. The flexibility and performance offered by this new generation of embedded storage blades suits them to many OpenVPX system applications, replacing large, power-hungry external RAID or file server boxes with a high-reliability, single-blade storage solution (Figure 1).