Given that 850evo uses 40nm class 3D nand, its highly unlikely, that it suffers from read degredation the same way 840 series does.
Actually we're talking about two different characteristics: one is maximum P\E cycles, the other one is data retention. The TLC cell might survive (almost) the same number of P/E cycles as a MLC cell on the same process geometry (say 19nm) but it may have drastically lowered data retention. However, seeing how the 250GB 840 drive died close to 1PB of writes, I would say the 300TB limit signaled by the wear leveling counter indicates a rather resilient drive.I agree. Also, after thinking about the fact that the 840 EVO seems to have really good endurance I am thinking the problem probably is with the controller programming.
Actually we're talking about two different characteristics: one is maximum P\E cycles, the other one is data retention. The TLC cell might survive (almost) the same number of P/E cycles as a MLC cell on the same process geometry (say 19nm) but it may have drastically lowered data retention. However, seeing how the 250GB 840 drive died close to 1PB of writes, I would say the 300TB limit signaled by the wear leveling counter indicates a rather resilient drive.
Meanwhile, my PM851 drive patiently awaits a fix, which will come even later than the one for 840 EVO, if ever
All we know for sure is if the manufacturer gives a consumer drive a TBW rating of say 70TB, that drive will have a power off data retention of at least 1 year at 30C after 70TB of host writes. Fun fact is simply storing the drive at 25C might double power off data retention. (see this doc, page 27)Honestly I don't know what the relationship is, if any, between endurance and data retention. I was assuming that perhaps the fact that the 840 EVO did do a rather remarkable 1PB of writes this could be an indication of it's ability to retain data? Is there a relationship between the two? I'm thinking about it now and I can see how they may not be related.
They did test data retention at some intervals, but they only left the drives on the shelf for 1-2 weeks: enough to spot a really weakened drive, but not much more.During endurance testing the drive is continually written to, and read, I suppose? Over and over. The written data is read rather quickly, and by that I mean months don't go by between writes and reads.
All we know for sure is if the manufacturer gives a consumer drive a TBW rating of say 70TB, that drive will have a power off data retention of at least 1 year at 30C after 70TB of host writes. Fun fact is simply storing the drive at 25C might double power off data retention. (see this doc, page 27)
Being able to withstand 1PB of host writes will surely indicate a rather conservative 70 TBW rating, but won't give any real info on data retention at say... 200TB.
They did test data retention at some intervals, but they only left the drives on the shelf for 1-2 weeks: enough to spot a really weakened drive, but not much more.
And where did I state otherwise?So TBW is usually a lot lower than an SSD can take before running out of write cycles.
And where did I state otherwise?
The power off data retention after a year is something that it should be able to do according to JEDEC standards after all the write cycles it is rated for is consumed.
And not when it has reached it's TBW rating.
And in that sentence it looks like you are equating the two.
Following on page 26:The SSD manufacturer shall establish an endurance rating for an SSD that represents the maximum number of terabytes that may be written by a host to the SSD, using the workload specified for the application class, such that the following conditions are satisfied:
1) the SSD maintains its capacity;
2) the SSD maintains the required UBER for its application class;
3) the SSD meets the required functional failure requirement (FFR) for its application class; and
4) the SSD retains data with power off for the required time for its application class.
This rating is referred to as TBW. Requirements for UBER, FFR, and retention are defined for each application class.
SSD endurance classes and requirements
Application Class: Client
Active Use (power on): 40°C, 8hrs/day
Retention Use: 30°C, 1 year
From the JEDEC SSD Specifications doc I linked above, page 25:
Following on page 26:
I bought a 1Tb 850 PRO SSD on 2 February.
For 3 weeks it worked really well, then Samsung's Magician software kept nagging me that a firmware update was available. I did nothing for a couple of days, but on 23 February, I gave in and applied the firmware. I turned off my laptop, but I was unable to boot to this SSD again. My laptop's BIOS/UEFI was unable to "see" the drive.
I have since discovered a large number of other 850 PROs have been "destroyed" by this firmware update including Xeon_Addict of this forum.
We have 250 members of a FB page created last Tuesday to collate worldwide victims of the deadly firmware update hoping to pressurise Samsung into responding appropriately. We are Samsung SSD 850 PRO firmware death if anyone else wants to share their experiences.
When we had no response from Samsung after nearly a week, we wrote this open letter to Samsung but again we have not had a response.
My recommendation is to avoid Samsung like the plague!
I did not say it's a data retention problem, but I did say TLC drives may have lower data retention than MLC drives. I don't now how Hulk arrived to the conclusion that Samsung TLC drives are not JEDEC compliant, and I'm sorry if it was somehow my doing.Why are people assuming it's a data retention problem, that of Samsung 840/840 EVO SSDs?
The key aspect of 3D V-NAND is the process node. By going back to 40nm lithography, the number of electrons increase exponentially, which makes TLC a much more viable technology than it was with modern planar NAND. Obviously, V-NAND doesn't change the basics of TLC NAND because it still takes eight voltage states to differentiate all the possible 3-bit outputs, but thanks to the increased number of electrons there is more breathing room between the states and thus the cells are more error tolerant.Samsung claims 10x reduction in voltage state overlaps, which is a massive change for the better. You can see how crammed the planar TLC voltage states are, so it's no wonder that the endurance is low because the states are practically overlapping at each point in the voltage distribution and hence even tiny changes in the cell voltage can alter the cell's voltage state.
PS: please, let's not turn this thread into another Samsung is bad / firmware bug / horrible RMA thread. If we were to judge all manufacturers by their mistakes, I don't think any of them would emerge unscathed. Well, maybe Toshiba would.The larger cell structure also enables higher performance because it takes less iterations to program a cell. With planar TLC NAND it took multiple very high voltage pulses as well as numerous verification process to reach the right charge, but with looser voltage distribution the programming process has less steps and thus takes less time.
I think the real confusion came from not having a proper term for the number of P\E cycles that leads to NAND cell death. We have "rated P\E cycles" to express the threshold for data retention, but when I wrote "maximum P\E cycles" earlier in the thread I meant the number of cell erases that leads to cell failure.The confusing thing (for most people) is that on consumer SSDs the TBW rating is most often not related with actual NAND endurance.
I did not say it's a data retention problem, but I did say TLC drives may have lower data retention than MLC drives. I don't now how Hulk arrived to the conclusion that Samsung TLC drives are not JEDEC compliant, and I'm sorry if it was somehow my doing.
From the JEDEC SSD Specifications doc I linked above, page 25:
Following on page 26:
I did not say it's a data retention problem, but I did say TLC drives may have lower data retention than MLC drives. I don't now how Hulk arrived to the conclusion that Samsung TLC drives are not JEDEC compliant, and I'm sorry if it was somehow my doing.
Anyway, trying to steer this thread back on topic, the main reason 850 Evo owners may not experience slowdowns on old data has to do with how much easier is to read&write data from TLC V-NAND.
Anandtech review
PS: please, let's not turn this thread into another Samsung is bad / firmware bug / horrible RMA thread. If we were to judge all manufacturers by their mistakes, I don't think any of them would emerge unscathed. Well, maybe Toshiba would.
And Toshiba?
Well it didn't take me long to find this: http://arstechnica.com/apple/2013/1...-fix-for-toshiba-drives-in-2012-macbook-airs/
I'm just wondering if 850 EVO owners are experiencing any read speed issues with their drives?