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What is QLC Flash

What is QLC Flash

What is QLC Flash?

Quad-level cell (QLC) flash is a capacity-optimized NAND memory technology that delivers a per-terabyte cost that matches or beats hard-disk drives (HDDs). As its name suggests, QLC stores four bits per cell, delivering NVMe performance with higher capacities.

QLC vs. SLC vs. MLC vs. TLC

QLC flash is the latest in a long trend of squeezing more bits per cell within a NAND flash device. Here’s a brief overview of how the technology has evolved over time:

  • Single-level cell (SLC) flash: One bit per cell, two possible voltage states
  • Multi-level cell (MLC) flash: Two bits per cell, four possible voltage states
  • Triple-level cell (TLC) flash: Three bits per cell, eight possible voltage states
  • Quad-level cell (QLC) flash: Four bits per cell, 16 possible voltage states

As can be seen, the number of possible voltage states doubles with each additional bit stored within a NAND cell. There’s an inherent tradeoff between capacity and complexity as you increase the number of bits you can fit within a single cell. 

Greater electrical precision is needed to account for the added complexity of managing multiple voltage states during read/write. In practice, this can translate to a reduction in performance and longevity of the NAND device. 

NAND endurance is measured in program/erase (P/E) cycles. So far, manufacturers have been able to produce QLC flash with 1,000 P/E cycles, which is orders of magnitude less than what’s possible with SLC flash (100,000 P/E cycles). 

However, performance and endurance are relative. Flash is still orders of magnitude more performant than HDDs, and there are work-arounds for dealing with the endurance limitations of QLC (e.g., using SLC flash as a cache). This same tradeoff slowed adoption of TLCs when they first appeared, but the technology improved over time, and today most enterprise flash storage arrays deliver high performance, reliability, and speed with TLC NAND. With the advent of QLC flash, it’s now possible to enjoy the speed of all-flash storage at a cost per capacity that can match or beat HDD storage arrays.

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The Benefits of QLC Flash

Common benefits of QLC flash memory include:

  • A lower total cost of ownership (TCO) for read-centric workloads
  • A reduced data center footprint
  • An exponential increase in capacity with the speed of all-flash

Why Choose Pure Storage for QLC Flash?

Pure Storage® FlashArray//C doesn’t use flash SSD modules like other storage vendors. Pure’s DirectFlash® modules allow raw flash to connect directly via NVMe, reducing latency and increasing throughput. This allows FlashArray//C to maximize the performance of its QLC flash modules while still delivering cost per capacity comparable to hybrid and HDD storage arrays. 

Other perks of using FlashArray//C for your storage needs include:

  • Evergreen™ Storage  for true non-disruptive upgrades with zero downtimes or data migrations 
  • A single pane of glass for managing all your storage resources both on premises and in the cloud with the Purity operating environment 
  • A modern data storage solution with the operational agility needed to handle both performance-sensitive and capacity-oriented workloads

NVMe performance at a lower cost with the industry’s first all-QLC enterprise storage array

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