Quantum Quantum Atlas 10K II 9.2/18.4/36.7/73.4 GB, Product Manual

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Feature Descriptions
Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives 6-9
6.16.3 Reallocation of Bad Blocks
Most of the spare blocks are located on the inner cylinders of the drive. All defective
blocks are in-line spared at the factory or at format time. Some spare blocks are
allocated at the end of each band, and are reserved for grown, revectored blocks. All
grown defects are reallocated to one of the spare blocks, using a “nearest neighbor”
algorithm.
If bad block replacement is enabled (via the AWRE and ARRE bits in the Read-Write
Error Recovery Page), blocks that are difficult to read or write may be replaced after
multiple retries.
If the bad block data is
recoverable
, the drive first verifies that the original block
location is bad with multiple write tests. If the write tests fail, the original data is
reassigned to a new location.
If the block’s data is
unrecoverable
, the block may or may not be replaced according
to the state of the RUEE bit in the Quantum Vendor Unique Page. If the RUEE bit
is set, the bad data is relocated with a Bad Data Mark appended to it. If the PER bit
is set in the Read-Write Recovery Page, operations resulting in bad block
replacement activate Check
6.17 THE ULTRA 160/m LOW VOLTAGE DIFFERENTIAL (LVD) SCSI
INTERFACE
SCSI-3 provides increased performance and versatility to SCSI disks. LVD uses
lower level voltage swings, differential signaling, and double transition (DT)
clocking to allow a maximum bus speed of 160MB/second in wide SCSI
configurations.
The Atlas 10K II disk drive supports the LVD/MSE (Multi-Mode LVD and Single-
Ended) interface standard. When installed on a bus with only LVD devices the Atlas
10K disk drive operates in LVD mode at transfer rates up to 150 MB/second. It is
fully compatible with Ultra2 LVD devices operating at slower transfer rates. If an
Atlas 10K disk drive is installed on a bus with one or more single-ended (SE)
devices, it automatically switches modes to operate in SE mode at the slower, legacy
data rates.
Differential SCSI operation has the advantage of higher reliability of data transfer
through increased immunity to electrical noise. Differential signaling uses a two-
wire active system in which current from each wire flows in opposite directions and
reverses direction for a signal transition. The direction of current flow determines
whether the voltage levels on the two wires have a high/low or low/high
relationship to each other. The common mode, or reference, level for the two LVD
signals is +1.25 volts. High and low is defined relative to this level. LVD permits a
wide range of signal amplitudes. The Atlas 10K interface drivers are designed to
provide a high to low range on each signal of approximately 400 millivolts in a
nominal configuration, resulting in a differential signal of approximately 800
millivolts.