Staggered Spinup; Activity Indication; Cacheflow; Write Cache - Western Digital WD1002FBYS Technical Reference Manual

Product Features WD RE3 XL333M
device to provide the host with an activity indication. According to the SATA spec, "Staggered
Spin-up Disable and Activity Signal shall not be enabled at the same time."

3.17.1 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.

3.17.2 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.
3.18

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.

3.18.1 Write Cache

CacheFlow is designed to improve both single and multi-sector write performance by
reducing delays caused by seek time and rotational latency.
The write cache adaptively detects random and sequential access patterns during application
execution.
If a defective sector is found during a write cache operation, that sector is automatically
relocated before the write occurs.
24 RELEASED 11/13/08 (WD CONFIDENTIAL) 2679-701179-A01