XL500S
Product Features
2679-701211-A06
RELEASED 10/21/10 (WD CONFIDENTIAL)
25
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.
3.15.1
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.
3.15.2
Read Cache
CacheFlow implements a multiple segment read cache. Cache segments are assigned to
read commands as they are received from the host.
Each read segment consists of pre and post read sectors in addition to the host-requested
sectors. This maximizes the amount of cache data in the drive’s buffer, thereby increasing the
likelihood of cache hits and improving overall performance.
3.16
48-bit Logical Block Addressing (LBA)
The 48-bit Address feature set allows devices with capacities up to approximately 281 tera
sectors or approximately 144 peta bytes. In addition, the number of sectors that may be
transferred by a single command are increased by increasing the allowable sector count to 16
bits.
3.17
Power Management
This drive supports the ATA power management commands that lower the average power
consumption of the hard drives. For example, to take advantage of the lower power
consumption modes of the drive, an energy efficient host system could implement a power
management scheme that issues a Standby Immediate command when a host resident disk
48-bit Address
Bits (47:40)
Bits (39:32)
Bits (31:24)
Bits (23:16)
Bits (15:8)
Bits (7:0)
LBA High (exp)
LBA Mid (exp)
LBA Low (exp)
LBA High
LBA Mid
LBA Low
16-bit Sector Count
Bits (15:8)
Bits (7:0)
Sector Count
(exp)
Sector Count
