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3.9
Fluid Dynamic Bearings (FDB)
Bearing design that incorporates a layer of high-viscosity lubricant instead of ball bearings in the hard
drive spindle motor. As an alternative to conventional ball bearing technology, FDB designs provide
increased non-operational shock resistance, speed control, and improved acoustics.
3.10
Staggered Spinup and Activity Indication (SATA Power Pin 11)
SATA device power connector pin 11 (see "Standard Factory Connectors" on page 12) is defined as a
means by the host to DISABLE staggered spinup and it may also be used by the device to provide the
host with an activity indication. According to the SATA II specs, "Staggered Spin-up Disable and
Activity Signal shall not be enabled at the same time."
3.10.1 Staggered Spinup
When multiple disks are installed in an enclosure, it is desirable to provide a simple mechanism by
which a subsystem controller can sequence hard drive initialization to minimize the current load
presented during power up. Staggered spinup provides this mechanism by preventing the hard drives
from spinning up until after successful PHY initialization (i.e., after PHY enters DP7:DR_Ready
state).
Staggered spinup is only applicable during initial power-up. If a drive is spun down using ATA
commands—as a result of having been placed in Standby or Sleep power modes, for example—the
drive shall spin up following the rules that govern spinup from low power modes described in ATA/
ATAPI-6 or later.
3.10.2 Activity Indication
The host controller through SATA power pin 11 may access storage device status and activity. The
signal provided by the device for activity indication is a low-voltage low-current signal. It is not suitable
for directly driving an LED. A buffer circuit external to the device must be employed to drive the LED.
The activity signal is based on an open-collector or open-drain active low driver. The device shall
tolerate the activity signal being shorted to ground.
3.11
CacheFlow™
CacheFlow is WD's unique, multi-generation disk caching system. It incorporates read cache with
write cache.
WD designed CacheFlow to obtain maximum performance with today's most popular operating
systems and applications. CacheFlow increases performance over prior caching algorithms by
increasing the number of times that requested data is in the cache. This reduces the number of host
commands that require actual media access thereby improving overall drive performance.
Typical applications perform a variety of access patterns, such as random, sequential, and repetitive.
CacheFlow is designed to dynamically adapt to the changes in access patterns that occur during the
course of application execution.
Random mode is the default operational mode for CacheFlow. Once CacheFlow detects a sequential
access pattern, it leaves random mode. CacheFlow also performs predictive read operations to increase
the probability that data requested in future commands already exists in the cache.
CacheFlow partitions the buffer into multiple segments to allow for the fact that applications may
access multiple non-contiguous areas on the disk. CacheFlow tracks the amount of valid data in each
segment and controls the deallocation of segments to maximize drive performance.
3.11.1 Write Cache
CacheFlow is designed to improve both single and multi-sector write performance by reducing delays
caused by seek time and rotational latency.
24
RELEASED 4/7/11 (WD CONFIDENTIAL)
WD Scorpio ML320S-AF2
2679-771320-A00
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