Quick Info on Samsung 860 QVO Drives

Lsacah on 24/04/2019 - 20:12
Last edited 07/05/2019 - 22:00

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.

Computing Computer Component Samsung SSD

Comments

Clear on 24/04/2019 - 20:25

+1

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.
- sacah on 25/04/2019 - 12:44
  
  Yeah, it's certainly a great use for them.
dcep on 25/04/2019 - 00:53

is qvo = qlc ?

is cache different from dram ?

is this dram-less ?
- sacah on 25/04/2019 - 12:45
  
  +1
  
  I've expanded the post with answers to your questions, also figured I'd add some more info people might be interested in.
Smokey010 on 02/05/2019 - 17:38

+2

This is very helpful. Cheers OP :)
Shwayne on 07/05/2019 - 14:57

It's also worth noting as a virtue of having less cells, it's quite obviously going to last less overall writes, which is of course reflected in the reduced warranty.
- sacah on 07/05/2019 - 22:04
  
  While true, I've added a bit more in-depth warranty section to talk about my views on this.
  - Shwayne on 16/05/2019 - 16:10
    
    Hey thanks, that's an awesome writeup, I might very well grab a 2TB one purely for installing games.
    
    With the P/E cycles being nice and high, I think the concerns is with the cells being more shared (by 25%?), so you'd expect to see them die 25% faster perhaps (since an arbitrary read is more likely to affect a cell)? or am I reading into it wrong.
    - sacah on 16/05/2019 - 23:07
      
      I couldn't think of a good heading to put this under that was generic enough, so I'll just reply to you (-:
      
      Thankfully reads on SSDs are free from a wear perspective. That said, frequently read cells can cause a charge to build up in surrounding cells, over time it can cause these cells data to be corrupted. Drives keep track of frequent reads and will move frequently read data to new, empty blocks to avoid this happening, or if the drive is filling, it could cause an erase, reprogram cycle to occur to stabilize the voltages across all the cells in that block.
      
      As far as the 25% faster wear from writes, while true when thinking about a single cell, remember it is only storing 4 bits per cell, we need 8 bits to make 1 byte, 1024 bytes to make 1 KiB and so on.
      Roughly speaking, cells are organized in pages, pages can be 8 to 16 kB in size, pages are organized into blocks. Blocks can be 4 to 8 mB in size.
      
      While SSDs can read/write to a page, they can only erase a block at a time.
      
      So while there is 25% extra storage space per block, we tend to store fairly large files these days, so probably not many blocks will get multiple files stored to them, and there are lots of techniques firmware has to avoid doing an erase cycle on a block if one of the multiple files gets deleted, though this is dependant on you leaving some space free on your SSD. I'd be confident that there wouldn't be any noticeable increase in wear compared to a TLC drive, provided you left 15%+ free space.
jace88 on 13/09/2019 - 21:54

Great thread. I keep looking at the 860 QVO 4TB hence why I keep posting deals when I see them but I'm still holding out until it falls further to the sub $400 range (I know, unlikely anytime soon) given that QLC was meant to bring about much cheaper SSDs. Let's see. It would make a great Steam and photo library drive.
- sacah on 13/09/2019 - 23:19
  
  +1
  
  Thanks, I'm pretty close to buying a 2tb, my 7 & 9yr old HDDs are getting a bit slow.