The INCITS T10 Technical Committee for SCSI Storage Interfaces

The InterNational Committee for Information Technology Standards (INCITS) has about two dozen Technical Committees that develop standards for both ANSI and ISO/IEC. T10 (, the Technical Committee for SCSI storage interfaces is the largest of these Technical Committees with a membership of nearly 80 organizations. All modern storage devices comply with one or more standards developed in T10.

Chaired by John Lohmeyer, T10 meets for one week six times a year at various locations mostly within the United States. About 80 people attend these meetings. Many STA members, who cover all areas of T10’s work including physical signaling, protocol standards, command sets, and the SCSI architecture model, attend.

Industry storage specialists frequently attend T10 meetings. They also receive a lot of help from other large storage OEMs, including STA member companies. Once they write a proposal, it is reviewed in the committee meetings until it is right. It’s not unusual for a proposal to be reviewed four or five times before the committee is willing to incorporate it into one or more draft standards.

T10’s work started with parallel SCSI and has grown to include:

  • The SCSI Architecture Model, which sets minimum requirements for SCSI standards.
  • Command sets for Block Devices (magnetic disks and solid-state devices), Stream Devices (tape drives), Medium Changer Devices (jukeboxes), MultiMedia Devices (CD ROMs, DVDs, Blu-ray), Controller Devices (RAID), Enclosure Services Devices, Object-Based Storage Devices, and Automation Drive Devices.
  • Physical and/or Protocol standards for parallel SCSI, Serial Bus Protocol (IEEE 1394), Fibre Channel Protocol, Serial Storage Architecture (SSA: mostly used within IBM), iSCSI, USB Attached SCSI (UAS: high-performance SCSI over USB), Serial Attached SCSI (SAS: parallel SCSI’s serial replacement), Automation Drive Interface (ADI: used for Automation Drive Devices, and most-recently, SCSI over PCIe® (SOP: defines a SCSI transport using PCI Express).

In addition to the standards mentioned above, T10 has three generations of standards for SCSI/ATA Translation: SAT, SAT-2, and SAT 3. These standards map SCSI commands to ATA (SATA) disk drives. Most operating systems internally are coded assuming SCSI-compliant storage devices. The SAT family of standards provides a common software mapping to the low-cost ATA/SATA hard disk drives. This effort necessitates a close relationship with a sister committee INCITS T13, the Technical Committee responsible for the AT Attachment (ATA) storage interface.
We are all aware of the USB flash drives we use to move files around. While these devices are wonderful for moving big files, they are relatively slow because they use the USB Mass Storage Model, which does not support command queuing (overlapped commands).

Without much fanfare, a recently published T10 standard, USB Attached SCSI (UAS) promises to deliver high performance when using USB storage. The UAS protocol supports command queuing and it fully complies with the SCSI Architecture Model. USB storage devices using UAS protocol deliver performance approaching that of SAS (but not the physical connectivity of SAS). Western Digital is now shipping Passport external hard drives that employ UAS drivers; these external drives perform nearly as well as internal SATA drives. Some say UAS drives may eventually replace internal SATA drives.

A big project within T10 this year is SCSI over PCIe (SOP) and PCIe Queuing Interface (PQI). This pair of standards is commanding a lot of attention not only within T10, but also from the Peripheral Component Interconnect Special Interest Group (PCI SIG) and various Solid State Device manufacturers. STA member companies are major contributors to these projects.

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