{"id":5649,"date":"2021-05-10T08:00:06","date_gmt":"2021-05-10T15:00:06","guid":{"rendered":"https:\/\/phisonblog.com\/?p=5649"},"modified":"2022-06-14T08:11:09","modified_gmt":"2022-06-14T15:11:09","slug":"qlc-nand-for-consumer-ssds-2","status":"publish","type":"post","link":"https:\/\/phisonblog.com\/ja\/qlc-nand-for-consumer-ssds-2\/","title":{"rendered":"\u30b3\u30f3\u30b7\u30e5\u30fc\u30de\u30fc\u5411\u3051SSD\u5411\u3051QLC NAND"},"content":{"rendered":"

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In the last decade, data has grown at an exponential rate due to technological advancement in the field of \u201cinternet of things.\u201d Exponential data growth requires advancement in the storage technology to store the generated date. Hard disk drive (HDD) and Solid-state drives (SSD), which are two main forms of storage in the modern computing system, have increased their storage capacity to meet the demand.<\/p>\n

HDDs industry now uses heat-assisted magnetic recording or microwave-assisted magnetic recording to increase drive capacity. SSD makers have addressed the demand for higher capacity by storing more bits per NAND storage cell.<\/p>\n

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NAND flash technology<\/h3>\n

NAND Flash technology started by storing one single bit per cell\u2014 and this cell is called Single Level Cell (SLC). SLC NAND provides high throughput, high endurance, and low latency, but has small capacity. NAND technology evolved and enabled storing two bits per call and it is called \u2014Multi Level Cell (MLC). MLC NAND provides twice the capacity of SLC NAND but has lower throughput and has less endurance. Further enhancement in the NAND technology enabled storing three bits per cell\u2014 and it is called Three Level Cell (TLC). TLC NAND has three times the SLC NAND capacity but has much lower throughput and endurance. The latest NAND technology stores four bits per cell\u2014 or Quad Level Cell (QLC). QLC NAND provides four times the SLC capacity but has much lower throughput and endurance.<\/p>\n

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How to address QLC NAND tradeoffs<\/h3>\n

QLC NAND addresses the increased capacity requirement but comes with tradeoffs of slower throughput and lower endurance. One way to address slower throughput and lower endurance of QLC is to add a small SLC cache on the drive. Data from the host is written to the SLC cache first, and then data is moved to QLC. Throughput seen by the host depends upon the workload. If the size of the data that is being written is smaller than the SLC cache size, then the host will see SLC throughput. If the data being written is larger than SLC cache size, then the combination of SLC and QLC performance will be seen.<\/p>\n

SLC cache can also address the endurance concern of QLC NAND for specific workloads. If the host is writing and rewriting specific Logical Block Address (LBA) range and the LBA range is smaller than the SLC cache size, then the data is invalidated in the SLC cache and only the final copy of the LBA is moved to QLC.<\/p>\n

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Read: The Benefits of Using SLC Buffers with SSDs<\/div><\/div><\/div><\/div><\/div>\n

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Maximize the benefit of using an SLC cache<\/h3>\n

To maximize the benefit of an SLC cache, NAND Flash supports using QLC NAND in SLC mode. In this mode, QLC cell will be used to store only a single only single bit. This will reduces the capacity by one fourth but provides throughput and endurance of an SLC cell. When used for a \u201cFresh Out of Box\u201d (FOB) drive or for applications that do not fill the drive completely, using this feature will enables a substantially bigger SLC cache, which in turn, can provide better throughput and endurance.<\/p>\n

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Consumer workload<\/h3>\n

The SLC cache benefit depends upon the workload. Can a QLC drive be a good fit with an SLC cache? Consumer drives have the following characteristics:<\/p>\n