Western Digital WD 2TB 3D NAND SATA III 2.5" Internal SSD (Retail) - Manual (Page 10)

Bad Block Management
Bad blocks are occasionally created during the life cycle of a flash component.
These bad blocks must be marked and replaced dynamically in order to prevent
read/write failures. When a bad block is detected, the embedded Bad Block
Mapping algorithm removes the block from future use.
Background Garbage Collection
The flash management firmware will perform internal housekeeping activities, such
consolidating and flushing the SLC blocks to the TLC storage or reorganizing the
data in the TLC array or SLC array. These activities are performed in the background
and are transparent to the host, thus improving performance while providing a
seamless user experience.
Tiered Caching
The WD Blue 3D NAND SATA SSD uses a tiered caching structure to improve write
performance and endurance.
Modern operating systems typically access the storage device using small access
blocks; the majority of these being 4KB. These access blocks are incongruent with
the physical block size (less than 1MB) of the newer generation of flash memory
technology, and writing directly to the TLC array is also slower than writing to SLC
blocks. To overcome these hurdles, the WD Blue 3D NAND SATA SSD employs three
storage layers:
▪ Volatile cache — DDR DRAM cache
▪ Tiered Caching structure — A non-volatile flash write cache
▪ Mass storage — TLC NAND flash
The tiered caching structure is a pool of X1 blocks which are used as write cache to
accumulate and consolidate all writes at high speed. It works in the background,
then flushes them into the larger X3 storage blocks and uses optimized write
transaction sizes to maximize endurance.
All host data is written to X1 blocks to achieve the highest performance. Three X1
blocks are copied sequentially into one X3 block during the flush to mass storage
when exceeding their threshold.
Low-Density Parity-Check (LDPC)
An enhancement introduced with the WD Blue 3D NAND SATA SSD is the low-
density parity-check (LDPC) error correction code (ECC) technology. LDPC
significantly improves reliability over the previous generation of BCH code,
supports progressive levels of error correction, and runs on-the-fly using a
dedicated hardware core to minimize latency and impact on overall drive
performance. Consequently, it uses less power than deeper dynamic read retries.
Advanced Power Management
The WD Blue 3D NAND SATA SSD includes an advanced power management
system that supports Device Initiated Power Management (DIPM). Host Initiated
Power Management (HIPM) has been disabled in the WD Blue 3D NAND SATA SSD.
Introduction
WD Blue 3D NAND SATA SSD
User Manual
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