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Yeah. QLC is bad but mature TLC with a DRAM cache can be an excellent choice b
by dannyw 7y ago
Yeah. QLC is bad but mature TLC with a DRAM cache can be an excellent choice b
- Nursie 7y agoQLC with a decent SLC cache seems to work just fine as well, for most consumer purposes - see drives like the sabrent Rocket-Q
- chx 7y agoI do not know whether it's actually possible but if you partitioned an 1TB Intel 660p to only 140GB and left the rest open would it make that into a 140GB SLC SSD? If so, then the 1 USD/GB for an SLC drive is an absolute bargain...
- Dylan16807 7y agoQLC with SLC cache is probably the best analogy for these drives, too. Some workloads will never have a problem, others will hit performance walls.
- baybal2 7y agoYou need 6 times more QLC chips to get an equivalent write performance to TLC on average. Of course, for NAS RAID arrays that were already saturated by TLC man times over, it makes little difference.
- Dylan16807 7y ago> You need 6 times more QLC chips to get an equivalent write performance to TLC on average. Depending on how you define average, yes. But a sufficiently bursty workload is always writing to SLC. How the drive performs in practice depends on where you sit on that spectrum.
- Nursie 7y agoBut if you have a large (hundred GB, for example) SLC/TLC cache and DRAM, then for most consumer use you're never going to see a difference.
- baybal2 7y agoStill, does it make a net improvement over TLC? Explaining: there are 100% TLC drives high in the benchmarks, as long as you look at 1tb+ category. You only need 3 times more chips with TLC than MLC, which was still easily doable, and there were no equivalent sized MLC chips anyways. Read speeds weren't a problem with any flash technology, but QLC will give you harddrive level read speeds at sizes below 1tb. QLC will only take off in SSD's sized 5TB+ if per-chip speed will not improve dramatically, like at least twofold. QLC + huge cache is not good deal cost wise in comparison to pure TLC.
- Nursie 7y ago> Still, does it make a net improvement over TLC? Speed-wise no, but it (almost) keeps up with the lower end of TLC NVMe drives. > QLC + huge cache is not good deal cost wise in comparison to pure TLC. Cost wise? Yes it seems to, Sabrent's "Rocket Q" is about the cheapest 2TB on the market, and performs pretty well, Reads more or less competitively with the non-QLC drives from the same vendor and writes at around 2/3 the speed. Intel's 660p range performs a little less well, but typically still multiple times as fast as SATA drives, and is generally cheaper too.
- marcan_42 7y agoQLC 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.