As enterprise and hyperscale environments continue their push toward higher storage density, quad-level cell (QLC) flash memory has become a key technology for increasing SSD capacity while improving cost efficiency. However, achieving the full benefits of QLC requires addressing one of its fundamental limitations - endurance. Mixed-media SSDs1 are emerging as an innovative solution that combines the capacity advantages of QLC with the performance and endurance benefits of pseudo single-level cell2 (pSLC), enabling a new class of high-capacity enterprise storage platforms.
Why Traditional Tiered Storage Is Becoming More Complex
For years, storage architects have relied on separate high-performance/high-capacity storage devices to balance workload requirements. Storage-class memory (SCM) or single-level cell (SLC) devices have typically handled metadata and latency-sensitive writes, while QLC-based SSDs provided less expensive bulk storage. While effective, these capabilities introduce additional complexities including having to manage multiple device types, conducting separate qualification and firmware management processes, and competing for limited PCIe® resources.
As SSD capacities increase up to 245 terabytes3 (TB) and beyond, the ability to scale separate performance and capacity tiers become increasingly challenging, requiring a more streamlined approach.
One Drive, Two Storage Personalities
A mixed-media SSD consolidates performance and capacity tiers into a single device. Using shared NAND resources, the drive creates two distinct namespaces:
- A pSLC namespace optimized for metadata, write buffers, cache operations and small random I/O.
- A QLC namespace optimized for bulk user data, sequential read operations and large aligned write operations.
This workload-aware architecture places data on the media best suited to its requirements. Metadata, write buffers and latency-sensitive operations benefit from the higher endurance of pSLC flash memory, while bulk data and large aligned write operations leverage the density and capacity advantages of QLC flash memory.
Reducing Write Amplification
One of the most significant benefits of mixed-media architecture is its ability to reduce write amplification (where the physical data written to flash memory is larger than the amount intended by the host system). Rather than writing small random I/O directly to QLC, incoming write operations are first absorbed by the pSLC namespace. Data can then be staged and reorganized into large sequential streams before being written to QLC. Combined with Flexible Data Placement4, this approach helps reduce unnecessary NAND activity, improve endurance and extend usable drive life.
Configuring the pSLC-to-QLC Ratio
A key implementation consideration is determining how much NAND capacity should be allocated to pSLC. Typical deployments dedicate 1% to 6% of total flash capacity to pSLC, balancing endurance against usable QLC capacity. The examples shown in the image below illustrate several common configurations for a 61.4 TB SSD, however, the pSLC allocation can be adjusted beyond these example values to meet specific workload requirements. Once configured, the pSLC-to-QLC ratio remains fixed for the entire life of the drive.
Configuration Trade-off Comparison using a 61.4 TB SSD
|
pSLC Percent
|
QLC Percent
|
QLC TB Capacity
|
pSLC TB Capacity
|
|
1%
|
96%
|
58.9 TB
|
.6 TB
|
|
2.5%
|
90%
|
55.3 TB
|
1.5 TB
|
|
5%
|
80%
|
49.1 TB
|
3.1 TB
|
Driving the Next Generation of High-Capacity Storage
As enterprise datasets continue to grow, storage solutions must deliver both density and durability. Mixed-media SSDs provide a practical path forward by combining pSLC and QLC within a single device, enabling intelligent workload placement, reduced write amplification, simplified deployment and improved storage efficiency. Rather than force organizations to choose between performance and capacity and paying a drive-slot tax when needing both, mixed-media SSDs demonstrate that both can coexist within a unified architecture designed for the next generation of large-scale storage deployments.
NOTES:
1 Mixed-media SSDs are advanced SSDs that integrate two or more different types of NAND flash memory, combining high-endurance SLC with high-density QLC within a single physical drive. This internal layering lets each SSD use the fast, durable tier for write-buffering and metadata, while routing bulk data to the high-capacity tier.
2 Pseudo-single level cell (pSLC) is a flash memory operating mode that configures cheaper multi-bit storage to act like high-endurance single-bit storage that boosts write speeds, lowers power use and increases a drive lifespan (endurance) up to 10 times when compared to standard triple-level cell (TLC) or multi-level cell (MLC) flash memory.
3 Definition of capacity – KIOXIA Corporation defines a megabyte (MB) as 1,000,000 bytes, a gigabyte (GB) as 1,000,000,000 bytes, a terabyte (TB) as 1,000,000,000,000 bytes and a petabyte (PB) as 1,000,000,000,000,000 bytes. A computer operating system, however, reports storage capacity using powers of 2 for the definition of 1Gbit = 230 bits = 1,073,741,824 bits, 1GB = 230 bytes = 1,073,741,824 bytes, 1TB = 240 bytes = 1,099,511,627,776 bytes and 1PB = 240 bytes = 1,125,899,906,842,624 bytes and therefore shows less storage capacity. Available storage capacity (including examples of various media files) will vary based on file size, formatting, settings, software and operating system, and/or pre-installed software applications, or media content. Actual formatted capacity may vary.
4 Flexible Data Placement (FDP) is an NVMe™ standard feature that lets a host system give a storage drive hints about where to store data. By grouping data with similar lifespans into the same physical flash blocks, FDP reduces wear on the drive, cuts power use, and improves performance.
TRADEMARKS:
NVMe is a registered or unregistered trademark of NVM Express, Inc. in the United States and other countries. PCIe is a registered trademark of PCI-SIG. All other company names, product names and service names may be trademarks of third-party companies.
DISCLAIMERS:
KIOXIA America, Inc. may make changes to specifications and product descriptions at any time. The information presented in this blog is for informational purposes only and may contain technical inaccuracies, omissions and typographical errors. Any performance tests and ratings are measured using systems that reflect the approximate performance of KIOXIA America, Inc. products as measured by those tests. In no event will KIOXIA America, Inc. be liable to any person for any direct, indirect, special or other consequential damages arising from the use of any information contained herein, even if KIOXIA America, Inc. are advised of the possibility of such damages.