The PCI SCSI option board is a half-length PCI board that provides expansion capability for qualified servers and graphics workstations of the Origin family, such as Origin200 and OCTANE workstations.
The board is available with either of two SCSI interfaces, differential or single-ended. Both interfaces support Ultra SCSI transfer rates and are compliant with ANSI Fast-20 standard X3T10/1071D and ANSI SCSI-2 standard X3.131-1994. Ultra SCSI (which adheres to the Fast-20 standard) is a 16-bit wide SCSI bus running at 20 MHz (40 MBps).
Figure 1-1 shows features of the differential PCI SCSI option board.
Figure 1-2 shows features of the single-ended PCI SCSI option board.
To determine if the board is single-ended or differential, see the icon near the connector, as shown in Figure 1-3.
The connector is terminated on the board.
This chapter describes
No cables are included with the PCI SCSI option board. (Cables are typically included with Silicon Graphics SCSI storage options.) Table 1-1 summarizes some Silicon Graphics SCSI cables that you can use with the board.
Table 1-1. SCSI Cables for the PCI SCSI Option Board
Marketing Code | Part Number | Length | SE/DF |
|---|---|---|---|
X-S-1M | 018-0546-301 | 1 m | SE/DF |
X-S-DF-10M | 018-0546-501 | 10 m | DF |
For pinouts for each type of connector for the PCI SCSI option board, see Chapter 2, “PCI SCSI Board Connector Pinouts.”
Board installation depends on the type of Silicon Graphics workstation or server you have.
O2000 and Onyx2 workstations and servers: contact your factory-authorized field service personnel.
All other applicable Silicon Graphics workstations and servers: see the owner's guide or installation guide. If you don't have these guides handy, the information is also online in the following locations:
IRIS InSight Library: from the Toolchest, choose Help > Online Books > SGI EndUser or SGI Admin, and select the applicable owner's or hardware guide.
Technical Publications Library: if you have access to the Internet, enter the following URL in your Web browser location window:
http://www.sgi.com/Technology/TechPubs/Once you are in the library, choose Catalogs > Hardware Catalog > and look under the Owner's Guides for the applicable owner's guide.
External SCSI devices can be
slow, Fast-10, or Fast-20
wide or narrow
single-ended or differential
Removable media SCSI devices are typically single-ended; Table 1-2 summarizes some of these important peripherals.
Table 1-2. Supported Removable Media SCSI Devices
Device | Internal | External |
|---|---|---|
CD-ROM drive | x | x |
Digital linear tape drive | x | x |
8-mm tape drive |
| x |
4-mm digital audio tape drive | x | x |
QIC (1/4-inch tape) drive |
| x |
Scanner |
| x |
Color laser printer |
| x |
 | Note: Make sure that the SCSI peripheral you wish to use is compatible with the PCI SCSI option board you have selected (single-ended or differential). |
This section explains
| Note: For information on setting up disks and filesystems, see the latest version of IRIX Admin: Disks and Filesystems. |
The PCI SCSI board supports one single-ended or differential channel that can connect to a single-ended or differential storage option, respectively. Such options include the Origin Vault expansion option, with its single-ended or differential storage capability. Each Origin Vault can contain up to six 3.5-inch disk drives (each 4.5 GB or 9.1 GB) as well as one or two 5.25-inch SCSI-2 peripherals. The 5.25-inch peripherals are single-ended; the 3.5-inch disk drives can be single-ended or differential, depending on whether the Origin Vault format has the differential converter board.
SCSI devices continue to evolve with higher bus bandwidths, faster data transfer rates, and channels with longer cables and more devices. A protocol establishes a SCSI bus's bandwidth, type, and data transfer rate. These factors are interdependent. For example, a 16-bit SCSI peripheral typically transfers more data at a faster rate than an 8-bit SCSI peripheral.
This section explains
A bus on a PCI SCSI board is 16 bits wide. The host system negotiates with the target SCSI peripheral as to how many bits of data to send in each clock: 8 (narrow SCSI) or 16 (wide SCSI). Regardless of how the bus is utilized, it remains 16 bits wide.
Since the default SCSI bus controller is 0, 8-bit buses use seven SCSI IDs for devices, and 16-bit buses use 15 SCSI IDs. For a differential PCI SCSI board attached to an Origin Vault, the Origin Vault's 3.5-inch disks are numbered 1 through 6 or 9 through 14.
In narrow mode, there may be eight target SCSI IDs, minus the number of IDs for hosts on the bus. The target IDs must not conflict with the host ID; if there is more than one host, their IDs also must not conflict with each other. Similarly, in wide mode, there are 16 target SCSI IDs minus the number of hosts. (The default SCSI bus controller ID can be reconfigured for dual-hosted SCSI operation.)
A SCSI bus type is either single-ended or differential. A single-ended SCSI peripheral uses inexpensive, open-collector wired OR busing configurations that use a signal comparison to ground. This design limits the distance the signal can be driven because of noise and speed considerations.
Differential SCSI peripherals use differential drivers and receivers with built-in hysteresis to provide improved signal noise immunity so that the bus can be driven greater lengths. Table 1-3 summarizes maximum cable lengths for the various SCSI options.
Table 1-3. Maximum Cable Lengths for SCSI Bus Options
| Maximum Total Cable Length for Entire Bus |
|---|---|
Differential Fast-20 | 25 m |
Differential Fast-10 wide | 25 m |
Single-ended (SCSI-1) | 6 m |
Single-ended Fast-10 (SCSI-2 or SCSI-2 Fast) | 3 m |
Single-ended Fast-20 (Ultra SCSI or Ultra SCSI-3) | 1.5 m |
Single-ended Fast-20 can support a maximum of eight devices, which must be evenly spaced along a 1.5-meter cable; a 3-meter cable can support a maximum of only four devices, evenly spaced. For PCI SCSI boards in the Origin family of systems, single-ended Fast-20 is used exclusively inside the host system; differential Fast-20 is used for external SCSI buses.
 | Caution: Single-ended and differential SCSI peripherals use incompatible integrated circuitry and cannot be mixed on the same bus. Converters can be used to isolate the bus segments. |
Data transfer rates are either slow or fast, measured in megabytes per second. An operation is either 8- or 16-bit in size; thus, data transfer rates are dependent on bus bandwidth. Figure 1-4 compares data transfer rates.
Data transfer rate is also affected by the media speed of the SCSI peripheral.
Fast-20 SCSI is not merely “fast SCSI.” The “-20” in the term signifies the maximum number of megatransfers (number of million operations per bus cycle, based on a bus's burst data rate) that can occur during an I/O operation, doubling the data rate. For example, an existing narrow 8-bit SCSI bus operating in fast mode can burst data at rates of 10 MBps; the same bus running Fast-20 SCSI can burst data at 20 MBps. An existing wide 16-bit SCSI bus in fast mode can burst data at 20 MBps, but the corresponding bus operating Fast-20 SCSI can burst data at 40 MBps.
These guidelines reflect the dependencies among SCSI bus bandwidths, types, and data transfer rates. Follow these guidelines to minimize inconsistent or inoperable SCSI buses:
Install single-ended and differential devices on separate buses.
In calculating SCSI bus length, include all cable length inside devices, components, and chassis.
For maximum performance, install wide and narrow SCSI devices on different buses.
To configure a SCSI channel, you must verify the type of SCSI protocol required (single-ended or differential, data transfer rate), identify each component in the SCSI channel, and obtain any missing components.
Because the system controller negotiates independently with the devices on a bus to establish the acceptable transfer rate of each device, you can mix fast and slow devices on the same bus. However, mixing narrow Fast-20 and wide Fast-20 devices on the same single-ended SCSI bus is not recommended.