In today’s digital age, the performance of storage devices directly impacts work efficiency and entertainment experience. Solid-state drives (SSDs) have become indispensable components in modern computers, and their technological advancements continuously enhance user data storage experiences.
However, the choice between cache SSDs and cacheless SSDs can be confusing. “IT Times” journalists delve into the differences between these types, from technical principles to practical applications, helping consumers choose according to their needs.
01
Terminology – Cache SSD
As the name suggests, a cache is a storage technology used for temporarily storing data. It acts as a component between fast and slow storage media, enhancing data access speed by storing recently or frequently used data. This concept first appeared in CPU design, such as L1, L2, and L3 caches.
In SSDs, cache (Cache) involves two different concepts: one is the physical component level, referring to the DRAM cache chip on the SSD; the other is SLC cache (Single-Level Cell Cache) implemented through software control. Both DRAM cache chips and SLC cache technology can significantly improve SSD read and write performance, but only those equipped with DRAM cache chips are called cache SSDs.
02
Principle and Technology Analysis – DRAM Cache Chip as a “Transit Station”
DRAM is a chip for dynamic random access memory, where data is lost when the power is off. In contrast, the NAND storage chip in an SSD is a type of non-volatile memory that retains data even when the power is off.
Modern SSDs typically use TLC (Triple-Level Cell) and QLC (Quad-Level Cell) NAND chips. While they excel in storage density, their read and write speeds (typically a few hundred MB/s for reading and tens to hundreds of MB/s for writing) cannot compare to the gigabytes-per-second high-speed read and write capabilities of DRAM.
One core responsibility of the DRAM cache in a cache SSD is to host the Flash Translation Layer (FTL) mapping table. Upon system startup, the mapping table migrates from the NAND chip to the DRAM, serving as a detailed map that indicates the correspondence between logical and physical addresses. This ensures the SSD can respond to data access requests efficiently, achieving fast addressing.
Additionally, the DRAM cache acts as an efficient “transit station.” Unlike traditional mechanical hard drives that can directly overwrite data, the write mechanism of NAND flash is more complex. It involves first reading old data, then erasing the storage unit, and finally writing new data. The DRAM cache can optimize this process by quickly storing data to be written and old data to be migrated, acting as a high-speed transit area and speeding up data processing steps. This mechanism significantly enhances the overall read and write performance of the SSD.
03
Principle and Technology Analysis – SLC Cache as a “Fast Lane”
SLC cache functions as a “temporary fast lane” in the data transmission path, using software control to temporarily emulate part of the NAND chip’s capacity as SLC mode. Compared to TLC and QLC, which store 3 and 4 bits of data per cell, respectively, SLC stores only 1 bit per cell. This simplifies the data read and write process, reduces access complexity, and provides faster read and write performance.
During large continuous write operations, the SLC cache area first handles these data, akin to vehicles speeding on an uncongested fast lane. Once the SLC cache fills up, data transfers to the TLC or QLC area at a regular speed, causing the SSD’s write speed to return to normal.
By intelligently managing data migration based on data usage frequency and access patterns, SLC cache technology ensures burst performance under heavy loads and reduces NAND chip erase and write cycles, thus extending SSD lifespan.
Different SSD manufacturers allocate different proportions of fixed SLC cache in their products, typically ranging from 10% to 50%. For instance, a 1TB SSD might have 100MB to 500MB allocated as SLC cache during use.
04
Practical Experience – Cache SSDs, Speed; Cacheless SSDs, Thermal Control
Compared to cacheless SSDs, cache SSDs show significant advantages in sequential read speed, sequential write speed, and 4K random read and write speed, especially in scenarios like operating system startup and application loading, making them suitable as system or game drives. The presence of a DRAM cache chip also reduces direct writes to the NAND chip, extending SSD lifespan.
However, in long-duration large file read and write scenarios, the difference between cacheless and cache SSDs is not significant, relying on SLC Cache strategies. A mature SLC Cache strategy can boost burst write performance and provide a streamlined FTL mapping structure, lower latency, and higher mixed read and write performance.
The power consumption and heat generation differences between cache and cacheless SSDs are more notable. Without the DRAM cache chip and slightly slower read and write speeds, cacheless SSDs excel in temperature control, often requiring only a surface heat dissipation sticker. In contrast, cache SSDs generate more heat during daily use and need thicker heat dissipation stickers.
05
Purchase Recommendations – Cache SSDs for Gaming PCs and Desktops; Cacheless SSDs for Enclosures and Laptops
Cacheless SSDs perform stably in office, home entertainment, and light gaming scenarios while maintaining lower operating temperatures and relatively lower prices, making them suitable for use in enclosures, laptops, and NUCs.
Cache SSDs, with their faster read and write speeds, are better suited for heavy gaming and professional applications. It’s advisable to equip cache SSDs with metal heat sinks and utilize device airflow for auxiliary cooling to prevent performance degradation or damage due to overheating.
Currently, the price difference between cache and cacheless SSDs of the same capacity and interface from the same manufacturer is less than 20%.
The higher price of cache SSDs is not just due to the additional DRAM cache but also because they use different controller chips and higher quality NAND chips. Manufacturers typically also provide better heat dissipation solutions.
For example, Samsung’s PCIe 4 interface cache SSD 990 PRO 2TB is priced at 1450 yuan, while the same capacity and interface cacheless SSD 980 PRO 2TB is priced at 1250 yuan.
Seagate’s PCIe 4 interface cache SSD FireCuda 530 2TB is priced at 1100 yuan, while the same capacity and interface cacheless SSD FireCuda 530R 2TB is priced at 900 yuan.
For domestic brands using domestic NAND memory, the price difference between cache and cacheless SSDs is even smaller. For instance, the DISKMFR series by YUNZE TECHNOLOGY LIMITED, the high-end PCIe 4 interface cache SSD D7000 2TB is priced at 1160 yuan, and the cacheless SSD D7100 2TB is priced at 1100 yuan.
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