Introduction, Specifications, and Packaging
QLC Flash hits the masses!
Flash Memory Summit 2018 is on, and it's rapidly looking like the theme of the year is 'QLC'. QLC stands for Quad Level Cell, which is a bit of a misnomer since there are actually 16 voltage levels of a QLC cell – the 'quad' actually relating to the four bits of data that can be stored at any specific location.
Doubling the number of voltage states allows you to store 33% more data in a given number of flash cells, but comes at a cost. The tighter voltage tolerances required and higher sensitivity to cell leakage mean that endurance ratings cannot be as high as TLC or MLC, and programming (writing) requires greater voltage precision, meaning slower writes. Reads may also see a slight penalty since it is more difficult to discriminate more finely grained voltage thresholds. SSD makers have been trying to overcome these hurdles for years, and it seems that Intel is now the first to crack the code, launching their first mainstream QLC SSD:
Specifications are not earth shattering but respectable for a budget-minded NVMe SSD. 1.8GB/s sequentials and 250,000 IOPS fall well within NVMe territory. The write figures may be higher than expected given this article intro, but Intel has a few tricks up their sleeves here that help them pull this off:
While not specifically called out in the specs, Intel has implemented a large dynamic write cache to help overcome slower QLC media write speeds. The idea here is that in the vast majority of typical usage scenarios, the user should never see QLC speeds and will only ever be writing to SLC. The dynamic cache is created by simply operating sections of the QLC media in SLC mode (1TB of QLC = 256GB of SLC). Intel could have gone higher here, but doing so would more negatively impact endurance since erasing blocks of cells wears the flash similarly regardless of the mode it is currently operating in.
Simple packaging. Nothing to write home about.
Read on for our full review of the Intel SSD 660p 1TB QLC SSD!
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