Solid State Storage Standards Explained

Standards are a necessity for any marketplace. In the data storage industry, standards define how components connect and communicate, which enables interoperability, and drives volume. The Solid State Storage (SSS) technology infrastructure is standards based, from the Flash chip interface to the software driver that interacts with the host operating system.

The diagram below depicts two types of SSS devices. On the left is an SSS device with an HDD-type interface, which connects via a separate Host Bus Adaptor (HBA) card to the host bus. On the right is an SSS device which integrates the HBA and connects directly to the host bus.

See the text below the diagram for explanations of the each of the standards involved in the design and testing of SSS devices.

1. Driver Interface
   • A key enabler for widespread acceptance of a peripheral device is a standard software driver for the host operating system. NVM Express (www.nvmexpress.org) provides a standard interface for drivers for SSDs with PCIe interfaces.  NVMe was developed by the Non-Volatile Memory Host Controller Interface (NVMHCI) Workgroup.  This specification was previously referred to as Enterprise NVMHCI.  NVMe is scalable and applies to Enterprise and Client applications.
   • Currently ongoing in the T10 (www.t10.org) committee is the development of SCSI over PCIe (SOP), an effort to standardize the SCSI protocol across a PCIe physical interface. SOP will support two queuing interfaces - NVMe and PQI (PCIe Queuing Interface).
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2. Host Bus
   • The Peripheral Component Interconnect Express is a widely implemented host bus and an SSS device interface.  The Peripheral Component Interconnect Special Interest Group (www.pcisig.com) oversees the development and ongoing enhancement of the PCI standard.
   • The SSD Form Factor Working Group (www.ssdformfactor.org) was formed to standardize enterprise SSDs with a PCIe interface, including the connector all in a HDD form factor, as well as the addition of surprise hot plug / unplug capability.
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3. Device Interfaces & Connectors
   • Drive interface standards are developed by three Technical Committees of the International Committee on Information Technology Standards (INCITS). INCITS is accredited by the American National Standards Institute (ANSI). 
     1) T10 (www.t10.org) is responsible for the development of the Serial Attached SCSI (SAS) interface
     2) T11 (www.t11.org) develops the Fibre Channel – Arbitrated Loop (FC-AL) interface
     3) T13 (www.t13.org) is responsible for standards relating to the AT Attachment (ATA) interface
   • SATA-IO (www.sata-io.org) is an industry consortium that develops the SATA specification, utilizing the ATA protocol developed by T13, as well as promoting SATA within the storage industry.
   • SATA-IO recently announced SATA Express, which utilizes PCIe as the physical transport, while maintaining compatibility with existing SATA software.          
   • The SFF Committee (www.sffcommittee.org) is an ad hoc group that creates connector standards utilized by other industry standards groups, such as those listed on this page.
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4. NAND Flash Interface
   • It used to be that designing in Flash devices from different manufacturers meant having to accommodate slightly different behaviors from each, complicating the overall design. This situation has been addressed by organizations dedicated to standardizing the Flash interface, thus simplifying Flash integration.
   • The Open NAND Flash Interface (http://onfi.org) has developed interface specifications and driven the interface down a path of steadily increasing performance.

   • Under the JEDEC JC42.4 subcommittee ( www.jedec.org/committees/jc-42), a Joint Task Group was created for JEDEC and ONFI to develop a joint standard for the Flash interface.

5. SSS Form Factors
   • SSS devices are available in many different sizes and formats.  SSSI has defined three major types of SSS devices:
     1) Solid State Drive (SSD) Solid state storage that may utilize traditional HDD form factors such as 3.5-inch, 2.5-inch or 1.8-inch. Solid State Drives typically use storage interfaces such as SATA, SAS, or Fibre Channel.
     2) Solid State Card (SSC) Solid state storage that resides on a printed circuit board and can utilize a standard card form factor such as a PCI card. A Solid State Card would typically use an interface such as PCIe. Compared to a Solid State Module, an SSC normally has a larger physical size, more capacity, and higher performance.
     3) Solid State Module (SSM) Solid state storage that resides in a Dual In-line Memory Module (DIMM) or similar form factor and may use a standard HDD interface such as SATA. A Solid State Module is typically smaller in physical size and has lower capacity and performance than a Solid State Card.
   • For additional information, see the SSS Form Factors page
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6. Data Security
   • Protecting data from unauthorized access has become increasingly important. A common feature of storage devices is the ability to encrypt the data that is stored on the device. It is necessary to have a standard means of managing access to the encrypted data.
   • Within the Trusted Computing Group, the Storage Work Group (www.trustedcomputinggroup.org/developers/storage) focuses on standards for security services on storage systems, including the development of standards and practices for defining security services across storage controller interfaces.
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7. SSS Testing
   • To compare the characteristics of SSS devices, standardized test methods are required.
   • The JEDEC JC-64.8 subcommittee (www.jedec.org/committees/jc-64) defines environmental aspects, electrical quality, reliability, and durability methods.  Descriptions of released specifications can be found at http://www.jedec.org/standards-documents/focus/flash/solid-state-drives
   • The SNIA Solid State Storage Technical Work Group has developed a SSS Performance Test Specification (SSS PTS) that enables the performance of SSS devices to be fairly compared.  The Enterprise and Client PTS documents can be found here.