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Quad-level cell flash is slowly making its way into the enterprise. And while you might think that as the latest generation of NAND flash, it would improve upon and replace previous generations, that isn't how it's playing out. QLC drives are more likely to replace HDDs for object and bulk storage than SSDs to improve performance in many data centers.
QLC storage cells, which hold four bits per cell, are the logical next step after NAND predecessors:
- triple-level cell (TLC) with three bits per cell;
- multi-level cell (MLC) with two bits per cell; and
- single-level cell (SLC) with one bit per cell.
Increasing the capacity of each cell with each progressive generation of NAND has had its advantages. Capacity is the main benefit: A QLC NAND cell can store more data than TLC, MLC or SLC cells. Holding more data per cell lowers the cost per gigabyte, which also has clear advantages. However, QLC storage's advantages come at a price -- the most obvious being performance and endurance.
With each succeeding level of NAND flash, latency for reads, writes and erasures has increased, slowing operations and making the drives less useful for many applications. And as more bits are crammed into a cell with each new type of NAND, the cells can handle fewer program/erase (P/E) cycles and wear out faster. With each succeeding generation, NAND becomes more use-case specific and less applicable to general and mixed-use workloads. For this reason, we're still seeing SLC-based drives used for more write-intensive applications.
Given all this, it's important to know the differences between QLC flash and other types of NAND, and those differences are in the details. Take our quiz to find out if you have the knowledge you need to use QLC drives in the right places and with the right workloads.