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Storage Architectures and Devices 109
4.3.1.5 SCSI Bus Width
Operation of both 8-bit and 16-bit devices on the same external SCSI bus is
not supported due to the termination and cabling restrictions.
Operation of both 8-bit and 16-bit devices on the same internal bus is
supported concurrently as long as 16-bit internal cable and 68-pin to 50-pin
interposers are used.
Mixed-width internal attachment is supported concurrently with single-width
external attachment as long as maximum cable length restrictions are not
exceeded.
4.3.2 Cabling the PCI Single-Ended Ultra SCSI Adapter
The maximum supported cable length for the PCI single-ended Ultra SCSI
adapter (# 6206) depends on what type of devices are attached and where
they are attached (to the internal or external connector). Device types are
classified as:
• Ultra SCSI SE – maximum transfer rate of 40 MB/s (one byte transfers)
• Ultra SCSI Wide – maximum transfer rate of 40 MB/s (two byte transfers)
For this adapter:
• The maximum supported cable length for configurations without any
SCSI-II Fast or Ultra SCSI devices is 6 meters (approximately 20 feet).
• The maximum supported cable length for configurations that include
SCSI-II Fast (but not Ultra) is 3 meters (approximately 10 feet) with the
exception of the 7027-HSC High Capacity Drawer, which can be attached
with up to 6 meters of cable.
• To ensure optimum signal quality for Ultra SCSI transfers, attachment of
multiple Ultra SCSI devices is only recommended for devices mounted
inside the system unit. To ensure optimum signal quality for Ultra SCSI
transfers, it is recommended that only Ultra SCSI devices be attached to a
backplane that is driven by a PCI Single-Ended Ultra SCSI adapter.
This default setting can be changed (using SMIT or the
chdev command) to
allow attachment of external Ultra SCSI devices, with the restriction that there
are no SCSI devices attached to the internal connector.
The Ultra SCSI Adapter (# 6206) has the following supported configurations:
• Internal Ultra devices running at Ultra speeds:
• Up to six Ultra devices attached to the internal port (dependent on
internal configuration and cabling)