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QLC with an SLC cache is the SSD equivalent of SMR. They are fine for read-mostly workloads but performance goes completely down the drain when you do random wr

QLC with an SLC cache is the SSD equivalent of SMR. They are fine for read-mostly workloads but performance goes completely down the drain when you do random writes. I've tried QLC drives for cheap cluster storage. It turns out one QLC drive was slower than 4 old HDDs. I had to go back to HDDs until I switched to TLC flash because they were faster. Tail latencies hitting one second on QLC. It's incredible how bad they are. We shouldn't even be calling them SSDs at that point, they don't even remotely live up to the performance expectations you might have from an SSD.

Nursie 7y ago
>They are fine for read-mostly workloads but performance goes completely down the drain when you do random writes. This doesn't come out in tests or consumer experience of the drives that have a significant cache, like the aforementioned "Rocket Q", which has a DRAM cache and a large SLC/TLC cache behind it. Cluster storage is not a mainstream consumer use. > We shouldn't even be calling them SSDs at that point Is the intel 660p range not an SSD? It significantly outperforms SATA SSDs.
wtallis 7y ago
> It turns out one QLC drive was slower than 4 old HDDs. Was that a consumer QLC drive with SLC cache or an enterprise QLC drive with no cache and firmware that actually cares about latency? Something like the Micron 5210 ION enterprise QLC drive should still have at least 20x the sustained random write performance of a single hard drive.