I see these drives often, usually people are unsure about some aspects, I was also curious, so I got some info together and thought I'd share.
Capacity | 1TB………. | 2TB………. | 4TB………. |
---|---|---|---|
DRAM (LPDDR4) | 1GB | 2GB | 4GB |
NAND | QLC | ||
SLC Cache min | 6GB | ||
SLC Cache max | 42GB | 78GB | 78GB |
SLC Writes | 520MB/s | ||
QLC Writes | 80MB/s | 160MB/s | 160MB/s |
Drive is slow once it exhausts the SLC cache
For the 1TB drive after you've written 42GB continuously it will slow down to 80MB/s until you give the drive time to write the contents of the SLC cache into the QLC memory.
More specifically, there is 6GB of fixed SLC cache, and it will then dynamically change some QLCs to pSLCs (pseudo-SLC), up to 36GB for the 1TB version. I couldn't verify this, though I'd assume the 36GB of pSLC cache takes away 144GB of storage space, as it's using 4bit cells as 1bit cells. I hadn't thought of this previously and just said it was a straight 42GB/78GB of storage space to leave free.
Reduced warranty period
Older drives had 5yr warranty, the QVO ones have 3yrs, though I think the TBW is a better marker of reliability. I've been using a Samsung 840 Pro for 6yrs now, it had a 5yr warranty, with 73TBW as the warranty cut-off.
In the 6yrs I've been using it as my boot drive it has written 31TB, and currently has a health of 86%.
The 1TB QVO drive, while only having a 3yr warranty, is rated for 360TBW. For most people, even as a boot drive, I think this is more than capable.
Further info on this at the bottom.
Slower
The 2TB drive seems to be the sweet spot for performance. The 1TB QVO is 16% slower over all than the 860 Evo, the 2TB QVO is only 8% slower as seen in UserBenchmark 860 QVO vs 860 Evo
Be careful when reading benchmarks of these drives, many benchmarks aren't in real world conditions. For the tests replicating real world results the QVO drives are pretty close to more expensive drives, 2 & 4TB ones even closer. So long as you don't fill the drive allowing it to dynamically increase its SLC cache.
QVO == ?
QVO stands for Quality and Value Optimized
How much free space to leave for SLC cache
Regardless of SSD, it's suggested to leave 20%-25% free space to allow fast writes due to having empty blocks to write too. This is plenty of space for the pSLC cache, it probably uses about 5-10% of free space at that level toward pSLC cache, though I couldn't find specifics about this implementation of TurboWrite.
In-depth warranty question
These next few paragraphs are more about QLC in general, it's hard to find specific information about each drive to compare.
To see the endurance of cells they measure it in P/E cycles, the number of program/erase cycles per cell.
SLC had a 100k P/E cycles, MLC had 10k P/E cycles, TLC had 1k P/E cycles. So it was expected that QLC would have about 100 P/E cycles, maybe a few hundred tops. This is probably where the idea of QLC being unreliable came from originally.
Over time there were improvements in TLC, for example, the Samsung 850 Evo 1TB (TLC) has tested to have ~2k P/E cycles. Mid 2018 people were talking about TLC being up to 5k P/E cycles. This improvement seems to have also carried over to QLC, at launch it was touted to have 1k P/E cycles.
Looking further at the Samsung 850 Evo 1TB, released in 2014, it's a TLC drive, ~2k P/E cycles, it has 5yrs warranty, and 150TBW. The Samsung 860 Evo 1TB, released in 2018, a more modern TLC drive, probably around 4k P/E cycles, also has a 5yr warranty and 600TBW.
And then look at the other QLC drives out there, Crucial P1, Intel 660p, and Micron 5210 ION, all have 5yrs warranty, with 200TBW for both the P1 and 660p, and, though the ION is vague, it seems to aim for a massive 1970TBW, this is for a 2TB version that also states 1.5k P/E cycles.
When I saw the 860 QVO having quite a high TBW compared to older TLC drives, and above the 660p and P1, both QLC drives, I thought maybe it wasn't endurance of the cells, but their ability to correctly hold their set voltage over a period of time, that was the reason for the 5yr to 3yr change. Though the P1 and 660p are marked as 5yr, which leads me to think it's just Samsung positioning the drive to not detract too much from their other drives.
Worth mentioning P/E cycles aren't the full story, SSDs have some extra cells hidden away that can be used when other cells become damaged, we don't know how much these QVO drives have. There are also cleaver software techniques with wear leveling etc that drive makers employ to enhance endurance. Only time will tell for sure.
Thanks for the write up it's good to know. If I was going to buy a QVO it'd be as a game drive for sure.