{"id":287,"date":"2020-03-26T13:14:17","date_gmt":"2020-03-26T11:14:17","guid":{"rendered":"https:\/\/tekmart.co.za\/t-blog\/?p=287"},"modified":"2020-03-26T13:21:19","modified_gmt":"2020-03-26T11:21:19","slug":"qlc-vs-tlc-nand-which-is-best-for-your-storage-needs","status":"publish","type":"post","link":"https:\/\/tekmart.co.za\/t-blog\/qlc-vs-tlc-nand-which-is-best-for-your-storage-needs\/","title":{"rendered":"QLC vs. TLC NAND: Which is best for your storage needs?"},"content":{"rendered":"Reading Time-approximately:<\/span> 4<\/span> minutes<\/span><\/span>\n

QLC flash memory is best for most read-intensive workloads, while TLC is suited to write-dominant workloads. Discover how QLC vs. TLC NAND are coexisting in the data center.<\/strong><\/h2>\n\n\n\n

By <\/p>\n\n\n\n

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Kurt Marko<\/strong><\/p>\n\n\n\n

Consultant – MarkoInsights – SearchMicroservices<\/a> <\/strong><\/p>\n\n\n\n

\t\n\t\n\tPublished: 06 Mar 2020<\/a><\/p>\n\n\n\n

IT professionals tend to see the march of technology as monotonic and\n progressive — always moving in one direction toward greater \nimprovement, however that’s measured. The impression is generally valid:\n No one makes CRT TVs, rotary landline phones or cassette recorders \nanymore because there’s no market for them given vastly superior \nreplacement technologies.<\/p>\n\n\n\n

However, sometimes there’s room for multiple generations of the same \nunderlying technology because of secondary differences like performance,\n reliability, durability, lifespan and cost. Such is the case with NAND \nflash memory, where the progression from single-level cell (SLC) to multi-level cell, triple-level cell (TLC)<\/a>\n and now quad-level cell (QLC) storage technology has left enough \nperformance gaps between them to allow space for the different forms of \nNAND flash in the modern data center.<\/p>\n\n\n\n

The fundamental trade-off between performance and capacity<\/a> is discussed in this earlier article; here, our focus is on the two highest-density technologies, QLC vs. TLC . You might think that because QLC, with four bits per cell, is an evolutionary extension that increases flash memory density by 33% it could completely replace TLC, with three bits per cell, for high-capacity SSD uses. However, TLC technology has improved in terms of durability and performance to create roles for both types of NAND. Read on to find out more about the QLC vs. TLC debate and why you might want both in your storage systems.<\/p>\n\n\n\n

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The throughput vs. endurance tradeoff<\/strong><\/h3>\n\n\n\n

Memory technology seldom gives you something for nothing; pushing \nthe boundaries in one direction usually sacrifices features and \nperformance in another dimension. The evolution of NAND flash memory<\/a>\n cell technology has resulted in the tradeoff of higher density through \npacking more bits per cell for slower I\/O throughput, higher read \nlatency and lower endurance.<\/p>\n\n\n\n

The tradeoff between throughput and endurance versus capacity and \ncost is the reason some storage systems still use SLC devices. The \ndurability of SLC devices makes them ideal for write-intensive \ntransaction processing workloads. However, the new classes of \napplications in machine learning, big data analytics and streaming media\n involve an increasing number of workloads that predominantly read data \nrather than writing it, minimizing the importance of flash durability<\/a>.<\/p>\n\n\n\n

QLC vs. TLC: The trend toward fewer writes per day<\/strong><\/h3>\n\n\n\n

According to research firm Forward Insights, fewer than 20% of SSDs \nsold last year were spec’d at more than one drive write per day (DWPD). \nBy 2023, estimates are that 85% of drives sold will be the low-duration \nmodels spec’d at one or less DWPD. A DWPD measures the total amount of \ndata written to a drive in proportion to its total capacity and is used \nto specify guaranteed drive endurance of five years. A 1 TB drive spec’d\n at one DWPD can sustain an average of 1 TB of data writes every day for\n five years.<\/p>\n\n\n\n

The trend toward fewer writes per day bolsters the case for QLC drives. They have the shortest endurance of any current flash device because of tight tolerances on the charge levels for each bit state in a memory cell along with tighter spacings and thinner insulating gates in leading-edge flash manufacturing processes.<\/p>\n\n\n\n

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You must be careful when comparing DWPD specs across device types, \nbecause it’s a relative measure that’s a function of total drive \ncapacity. As Micron Technology points out<\/a>,\n a 960 GB TLC SSD rated at 1 DWPD has similar overall endurance to a \n1.92 TB QLC SSD rated at 0.5 DWPD for a particular workload. Although \nthe QLC DPWD spec is lower, the total amount of data that can be written\n per day is the same for the two devices. Thus, for workloads that \nalmost exclusively read data, the QLC device is a better choice because \nof its increased capacity.<\/p>\n\n\n\n

How QLC and TLC complement each other<\/strong><\/h3>\n\n\n\n

The QLC market is focused on read-dominant workloads; it’s not \ntrying to displace TLC devices, but rather to replace HDDs. This is \nMicron’s justification for continuing to manufacture both types of \ndevices. Micron has made a compelling argument that TLC and QLC are \ncomplementary, with QLC filling the gaps between TLC flash and HDD \nmagnetic disks. Indeed, Micron makes the case that because SSDs don’t \nwear when reading data, whereas HDDs do, QLC endurance is superior to \nHDDs for workloads where the data write pattern includes a high \npercentage of large sequential transfers.<\/p>\n\n\n\n

We can more precisely delineate the workload characteristics best \nsuited to QLC vs. TLC drives by looking closely at the I\/O patterns of \nvarious applications. According to Micron modeling, QLC drives are best \nfor read-intensive workloads<\/a>\n until the read\/write mix reaches about 70\/30 for small or random data \ntransfers, with the ratio reaching 50-50 for applications with large \nsequential writes. Conversely, TLC drives are better for write-dominant \nworkloads, except for the minority of heavily transactional applications\n that might require an SLC drive that can handle 5 or 10 DWPD.<\/p>\n\n\n\n

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Fortuitously, many of the enterprise applications experiencing the \nfastest growth and highest uptake have a preponderance of data reads \ncompared to writes. These include:<\/p>\n\n\n\n