3.13.1 Write Cache; 3.13.2 Read Cache; 48-Bit Logical Block Addressing (Lba) - Western Digital WD15NPVX Technical Reference Manual

WD Green MB500M-6Gb Product Features
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.

3.13.1 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.

3.13.2 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.

3.13.3 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.
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
Sector Count
(exp)
2679-771422-A00 RELEASED 5/2/13 (WD CONFIDENTIAL) 19