Quantum 10K II - Manual (Page 313)

Feature Descriptions
6-12 Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives
6.17.4 CYCLIC REDUNDANCY CHECKING
When transferring data with DT clocking on the SCSI bus, a significantly improved
form of error checking, cyclic redundancy checking (CRC) is used instead of the
traditional parity checking. With CRC checking, the device sending data generates a
four-byte CRC character based on the contents of the bytes being transferred. The
receiving device also generates a CRC character as it receives the bytes. At the end
of a data burst, the sending device transfers its CRC character and the receiving
device compares the sender’s CRC with its own. If the two CRC characters match,
then the data burst transferred without error.
In ST mode, the Atlas 10K II disk drive uses the traditional parity checking method
to ensure error free data transfers.
6.17.5 DOMAIN VALIDATION
A new feature in 160/m interface is the capability of the intiator and target devices
to execute a test sequence of commands before customer operation begins to ensure
that the SCSI bus can support the desired transfer rate. If errors are found, the
initiator can negotiate different transfer parameters until a working configuration is
found.
• Domain validation can detect configuration problems such as:
• Wide devices with a narrow bus segment between them
• DT devices connect through an ST expander
• Broken connections
It may also detect poor quality cables, marginal quality signals, and improper
termination.
Domain validation is implemented using standard SCSI commands and new
versions of the WRITE BUFFER and READ BUFFER commands. The sequence of
commands used for domain validation may vary from system to system. The selection
of commands used is entirely under control of host firmware and software.
6.18 HOT PLUGGING/REMOVAL AND INSERTION OF SCSI DEVICES
The Quantum Atlas 10K II SCA low voltage differential (LVD) disk drives are
designed for use in “Hot Swap” applications within a properly designed and
configured SCSI system. With care, system integrators can design storage arrays
and/or SCSI buses using Quantum Atlas 10K ii disk drives that are “Hot Swap Case
4” tolerant.
Case 4 is defined as follows:
• Devices are powered and the bus may have active I/O processes ongoing, but the
device being removed or inserted must be idle (no ongoing I/O processes during
the insertion/removal).
• Ground connections to the drive must be made and maintained for 1 millisecond
before, during, and 1 millisecond after the insertion/removal. The SCA-2
connector used on the Atlas 10K II disk drive meets this requirement.
• Device circuitry connected to bus pins must remain “glitch” free during power
up or power down.