Facebook parent Meta is exploring the use of QLC flash as an additional storage tier in its datacenters to address growing volumes of data as it juggles performance maintenance and energy efficiency.
Zuck's empire says in a blog posting that it is looking to deploy Quad Level Cell (QLC) SSDs as a middle tier between hard drives (HDDs) that provide bulk storage and the Triple-Level Cell (TLC) drives installed as a performance tier.
This is necessary, it claims, because HDDs continue to expand in capacity, yet their I/O performance hasn't been keeping pace. This means the bandwidth per terabyte has continued to decrease, forcing IT staff to meet performance needs by shifting hot data to a TLC flash tier, or by over-provisioning on storage.
QLC flash is less common in enterprise environments than TLC because of its slower performance and shorter endurance. Both are linked to the number of bits per cell. However, the higher number of bits per cell means QLC SSDs can have higher capacities and match HDDs on per-terabyte costs.
According to Meta's engineers, QLC occupies a "unique space" in the performance spectrum between HDDs and SSDs for servicing workloads that "depend upon performance at 10 MB/s/TB range i.e., where we had 16-20TB HDDs."
"Additionally there are workloads doing large batch IOs which do not need very high performance but still are in the 15-20 MB/s/TB range and use TLC flash today," it adds.
Meta is likely to have different workloads with different data access profiles when compared to the average enterprise, so its research and engineering efforts to create a QLC storage tier may not be applicable to other businesses.
Work is underway with storage vendors to integrate QLC storage into its datacenters. In particular, this includes Pure Storage, which uses its own NAND flash modules in its storage systems to try to up reliability and extend the drive's lifetime.
It isn't just a case of procuring a bunch of QLC SSDs and slotting them into servers. Meta says it will need to adapt its storage software layer to make use of the new storage tier.
Meta says it sees the primary benefit of QLC drives as byte density at the drive and server level and the associated power efficiency. The target for byte density of a QLC-based server is 6x that of the TLC-based servers it currently builds, it claims.
"Scaling such high throughput across CPU cores and sockets requires careful placement of data and compute to process that I/O. We need to make sure we minimize data touchpoints and can separate the I/O by type," the blog states.
For this reason, it appears Meta will choose DirectFlash Modules and the accompanying DirectFlash software from Pure Storage to make QLC storage reliable enough.
As memory suppliers continue to improve QLC designs and boost production output, Meta is banking on cost improvements, making this type of storage viable across a broader range of datacenter workloads.
Last year, Chinese memory biz YMTC claimed to have extended the endurance of QLC flash to match that of TLC, for example. ®