SCSI is a flexible I/O bus that is used in the design of a variety of peripherals, including disk drives, CD drives, tape drives, magneto-optical drives, and scanners. This section presents the requirements for SCSI hardware that is compatible with Windows NT, including adapters, peripherals, and any device that uses a SCSI controller.
| Windows NT Server | Enterprise Edition | Small Business Server | |
| Basic Server: | Recommended | Required | Recommended |
| Enterprise: | Recommended | Required | Recommended |
| SOHO: | Recommended | Required | Recommended |
Recommended: Fibre Channel, especially for servers running Windows NT Server/Enterprise Edition.
Note: Servers that implement Fibre Channel as the storage connection are not required to also provide SCSI capabilities.
The SCSI host adapter is the circuitry that serves as an interface between the system and one or more SCSI peripherals. A host adapter can be a card that plugs into the system’s expansion bus, such as a PCI card, or it can be designed directly into the system board set.
The host controller must support PCI bus mastering, with bus mastering enabled by default.
Required
Multi-initiator support allows two SCSI controllers—each installed in a separate computer system—to coexist on a shared SCSI bus with a set of shared devices.
For use in a system intended as a node in a cluster using shared SCSI, the SCSI IDs must be changeable from the default SCSI controller ID of 7, and the boot time SCSI bus reset operation must be able to be disabled on each controller attached to a shared bus.
For any SCSI controller with external connectors that is capable of being used as a node in a cluster, as described previously, the connector must be clearly labeled as available for cluster connections. This labeling must be positioned so that it is clearly visible to a user when attaching external devices to the affected external connector.
Required
Plug and Play SCSI host adapters must support virtual DMA services in the host-adapter option ROM, together with the required bus-mastering support. Virtual DMA supports scatter/gather capabilities, solving the problem of mapping linear addresses (segment:offset) into physical addresses.
Required
Connectors for each Fibre Channel or SCSI adapter, peripheral, cable, and terminator must be clearly labeled to show the bus type. All external SCSI connectors must display the appropriate SCSI icon defined in Small Computer Interface (SCSI-3) Parallel Interface (SPI) specification, Annex F, plus any clarifying abbreviations or acronyms. The following shows the related acronyms and their definitions:
Required
Without DIFFSENS, the differential bus drivers or a single-ended device will suffer fatal thermal damage if a single-ended device is put on a differential bus.
The specification for DIFFSENS is defined in Section 5.4.2 of the SPI standard.
Required
Parallel SCSI add-on adapters and on-board controllers must use automatic termination that allows a user to add external devices without removing the server case. Terminators used in the SCSI host adapter must be regulated terminators, which are also known as active, SCSI-3 SPI, SCSI-2 alternative-2, or Boulay terminators. SCSI termination built onto internal cables must meet the SCSI-3 specification.
Required
The host adapter must supply terminator power (TERMPWR) to the SCSI bus for system-board implementations using PCI or another expansion bus. All terminators on the external SCSI bus must be powered from the TERMPWR lines in the SCSI bus.
In addition, the circuit that supplies TERMPWR must have overcurrent protection built into it. Devices that provide TERMPWR must also provide some means of limiting the current through use of a self-resetting device. For example, a positive-temperature coefficient device or circuit breaker can be designed into the circuit. These devices open during an over-current condition and close after the condition ends.
Required
If an external connector is implemented, it must meet the requirements defined in SCSI-2 or a later specification.
Required
All SCSI peripherals and the SCSI host adapter must implement the SCSI bus data protection signal defined in the SPI standard, and data protection must be enabled by default.
Required
For internal and external configurations, the SCSI bus cable must be plugged into shrouded and keyed connectors on the host adapter and devices. This ensures that the cable is properly positioned so the user cannot plug in cables incorrectly. For internal configurations, pin 1 orientation must be designated on one edge of the ribbon cable and also on the keyed connector for the SCSI peripheral device.
For an external configuration, the SCSI connector must not use the same connector type as any other non-SCSI connector on the system.
Required
The recommended implementation for an external SCSI peripheral device is to provide automatic termination. In the absence of automatic termination, a mechanical means must be provided for setting termination and the switch must be accessible to the user without opening the server case or device chassis.
Required
Device connectors must meet the specifications defined in SCSI-2 or later.
Required
If SCAM support is present, it must be disabled by default. SCAM is not supported by the Windows NT operating system; enabling SCAM can cause the system to become unstable or inoperable.
Required
The hardware in SCSI peripherals must be able to fully recover from a software-initiated spin down without rebooting the system or cycling power. To properly support power management on SCSI drives and to ensure that the operating system responds to appropriate driver calls, be sure to correctly implement the STOP/START UNIT command as defined in the SPI (SCSI-3) standard.
Recommended
Wherever appropriate, for example, for storage disks, the STOP UNIT command can be used to decrease power consumption of the base platform.
Required
To ensure reliable support for hot-plugging capabilities, the following requirements must be met by any SCSI devices that allow hot-plugging:
In order to properly function with the native support in the operating system, developing industry standards such as those referred to as PCI Hot Plug and Compact PCI must use ACPI-based methods for supporting hardware insertion and removal as defined in the ACPI 1.0 specification.
Recommended: A locking mechanism to ensure that devices are removed only under operating system control or during sleep or off states. For implementation details and additional design guidelines, see the article about hot-plugging support at http://www.microsoft.com/hwdev/busbios/rem_devs.htm.