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Ryu Connor
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Samsung 840 & 840 EVO Bug

Sat Sep 20, 2014 11:08 am

http://anandtech.com/show/8550/samsung- ... on-the-way
http://www.overclock.net/t/1507897/sams ... -the-drive

AnandTech wrote:
For those who are not aware of the issue, there is a bug in the 840 EVO that causes the read performance of old blocks of data to drop dramatically like the HD Tach graph below illustrates. The odd part is that the bug only seems to affect LBAs that have old data (>1 month) associated with them because freshly written data will read at full speed, which also explains why the issue was not discovered until now.


Could a retention issue where ECC has to get involved cause this sort of impact?
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Musafir_86
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Re: Samsung 840 & 840 EVO Bug

Sat Sep 20, 2014 8:09 pm

-Excuse me, but aren't ALL SSD (and NAND flash storage) have wear-leveling algorithm that supposed to move around (shuffle) the data internally? So those old data never get shuffled at all?

-What about data retention? What'll happen to the data in a drive that has been unplugged for months/years?

-And how about the earlier 840 (non-EVO, non-Pro) which use 21nm TLC NAND (versus 19nm TLC NAND in 840 EVO)? Does it has the same issue too? I helped a relative upgraded his ProBook 6555b to a 120GB 840. :(


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drsauced
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 12:28 am

Same boat, I suggested the 840-EVO to my boss for his new machine, too. I'd hate to ruin his honeymoon with the drive with this news. Let's see how the 'validated' patch works out :)
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Flying Fox
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 2:11 am

Musafir_86 wrote:
-Excuse me, but aren't ALL SSD (and NAND flash storage) have wear-leveling algorithm that supposed to move around (shuffle) the data internally? So those old data never get shuffled at all?
Data that have not been modified are not actively rewritten to different cells, since this will just end up wasting write cycles on the current (probably just the block that stores the file metadata/entries) and the new cells (new metadata and the file contents). Wear leveling basically means when new data needs to be written, it will prioritize to write to blocks that have been written the least amount of times.

Musafir_86 wrote:
-What about data retention? What'll happen to the data in a drive that has been unplugged for months/years?
That's what the retention tests that TR conducts are for.

This one is interesting, the 840 and the 840 EVO have been on sale for more than 2 months. So perhaps this is the problem of a recent batch and/or a recent version of the firmware? Or it is because the promotions that newegg has been running such that a whole lot more people bought into the EVOs and are finally seeing the issue? I bought one during the period too but I did not have time to put it into production yet. So I still have time to wait for the patch before doing a real install on the thing.
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Ryu Connor
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 3:34 am

Benchmarks tend to be run on fresh drives, not on drives that have accumulated data over time and had that data age. Even TR's retention tests only go a week, which falls short of running into this bug.
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Flying Fox
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 4:10 am

Ryu Connor wrote:
Benchmarks tend to be run on fresh drives, not on drives that have accumulated data over time and had that data age. Even TR's retention tests only go a week, which falls short of running into this bug.

I mean many people have bought these drives more than 2 months ago. They probably have rebooted their systems or launch the same apps/games too. How come they did not report the problem? That's why I suspect a particular batch and/or a specific firmware version.
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Pholostan
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 5:55 am

Allyn Malventano has written a piece on on over at PCPer:
http://www.pcper.com/reviews/Editorial/ ... -over-time

Possible causes:

By this point you may be asking what the heck can be causing this? Here's my hypothesis:

1. Over time, flash cell voltages slightly drift.
2. Flash circuitry is designed to compensate for this by varying the read voltage thresholds and using varying levels of error detection and correction mechanisms.
3. Some unforeseen coordination issue between the flash and the controller, in the face of #2 above, is resulting in slower than normal read speeds for flash that has been storing data, undisturbed, for weeks or months.

Now I know there are many folks from many threads, that having read the above, are saying 'no way, it has to be worse than that!'. No, it doesn't. Why? Because out of all of the dozens or hundreds of folks running these tools and tests, not one has reported a single unreadable sector. Think about it, dozens of people are intentionally reading all data from these drives, which is way more than a user would be doing in typical use, and despite the slowdowns - no errors. If the flash cells or stored voltages were actually degrading so badly over time, the oldest stored data would likely be unreadable. Instead we see a steady speed taper down to a seemingly fixed (~50-100MB/sec, varying with drive capacity / die count) read speed. That indicates to me that the issue is one that can be corrected - maybe even in a manner that would snap speeds back to near full simply by updating the firmware. This is certainly possible, as we've seen it happen before.
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Ryu Connor
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 10:18 am

Flying Fox wrote:
I mean many people have bought these drives more than 2 months ago. They probably have rebooted their systems or launch the same apps/games too. How come they did not report the problem? That's why I suspect a particular batch and/or a specific firmware version.


If you dig into the thread, they find posts/complaints from people months and months ago. They also find that firmware version doesn't matter.

Sometimes issues take a while to notice. It's not the norm for people to just randomly benchmark their drive. It's not conclusive of course, but this issue may have always existed.
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CeeGee
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 2:10 pm

I use my 840 to hold my steam game library not for my OS drive. I downloaded HDTach to see what my drive was doing.

Image[/url]
This drive is currently holding about 206GB of data. It seems that as steam updates games and files get re-written the speed gets reset back to normal.

As a comparison here is my 830 drive that currently hosts my OS.
Image

I probably haven't noticed anything wrong because my OS drive is still working great and the games I'm playing have been recently updated and load fast still.
Last edited by CeeGee on Mon Sep 22, 2014 5:02 pm, edited 1 time in total.
 
danny e.
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 8:06 pm

Image

210GB of used space.

Edit:
I do have my settings on "maxium reliability" whatever that does. So, that might impact it a tiny bit but not to the extent it's dropped.
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Deanjo
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 9:01 pm

Damn I wish I could find the posts that I put in TR comments about this a year or so a go just so I could say "SEE I TOLD YOU SO!!!"
 
morphine
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Re: Samsung 840 & 840 EVO Bug

Sun Sep 21, 2014 9:22 pm

Image

Yeah, there might a problem.

This explains why it feels like my PC takes a bit longer to start up than it did, and when I bring up VMs to periodically update them, cleaning and compacting the virtual hard drives takes way longer than it should.
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CeeGee
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Re: Samsung 840 & 840 EVO Bug

Mon Sep 22, 2014 5:02 pm

After moving the data off the drive and then back on I got this.

Image
 
ozzuneoj
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Re: Samsung 840 & 840 EVO Bug

Mon Sep 22, 2014 10:15 pm

My 840 EVO 256Gb is exhibiting this problem as well. HDTach shows huge fluctuations between 30MB\sec and 400MB\sec.

*sigh*

I guess we should be glad that most of the files that load at startup are tiny and scattered, which is what made the low latency of SSDs so good to begin with.

Also, I bought my drive on Cyber Monday last year, so its about 10 months old.

There seem to be a lot of people using this to refresh the drives to get them back up to normal performance:
http://www.puransoftware.com/DiskFresh.html

I'm trying it now, though it is a bit annoying that I just installed like 30GB of games from my Steam catalog yesterday.

I don't recommend doing this too often on an SSD, but hopefully it'll smooth performance out again until they've released an official fix for it.
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Pholostan
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Re: Samsung 840 & 840 EVO Bug

Wed Sep 24, 2014 12:55 pm

Allyn and BrainSplatter seems to have a working theory:
http://www.pcper.com/reviews/Editorial/ ... pdate-Temp
After the initial posting of this article, further details have come to light. BrainSplatter got back to me with some data on temperature effecting the slowing effect on old file read speeds. The same test was run first at 32C (90f) and then at 52C (126F), here were his results:

Newest: 510 -> 507 MB/s = - 0.8%
2 weeks old: 477 -> 427 MB/s = - 10.5%
3 weeks old: 278 -> 211 MB/s = - 24%
4 weeks old: 289 -> 177 MB/s = - 39%

The temperature difference he used was a bit on the extreme side, but it did certainly show a speed delta that amplified with file age. This supports the theory that the EVO's controller is busy crunching ECC data, and as a result is running up against its Dynamic Thermal Guard Protection, which in this case is proportionally clocking the MCX controller / CPU slower in hotter environments.


Allyn has replicated the tests and come to similar results:
We can draw a few conclusions here:

* The flash itself is not degrading under higher temperatures, as the speed bounces back once the drive is cool.
* The controller was likely not meant to run at this sort of continuous ECC load, which further supports that a firmware fix might correct the issue (programmatically compensating for cell drift over time can mitigate the need for heavy ECC calculations and would theoretically restore speeds to near full for old files).


Sounds good to me that the problems likely will go away with a firmware fix. I bought a EVO just a couple of weeks ago.
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danny e.
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Re: Samsung 840 & 840 EVO Bug

Sun Oct 19, 2014 8:49 pm

danny e. wrote:
Image

210GB of used space.

Edit:
I do have my settings on "maxium reliability" whatever that does. So, that might impact it a tiny bit but not to the extent it's dropped.


After fix:
Image
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Flying Fox
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Re: Samsung 840 & 840 EVO Bug

Sun Oct 19, 2014 9:16 pm

danny e. wrote:
After fix:
Image

The fix is available officially now?
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morphine
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Re: Samsung 840 & 840 EVO Bug

Sun Oct 19, 2014 9:42 pm

Yeah, there's even some news about it in this obscure site.

http://techreport.com/review/27212/sams ... h-old-data
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Flying Fox
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Re: Samsung 840 & 840 EVO Bug

Sun Oct 19, 2014 9:44 pm

morphine wrote:
Yeah, there's even some news about it in this obscure site.

http://techreport.com/review/27212/sams ... h-old-data

Did not read the "Update" paragraph. Doh. :oops:
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just brew it!
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Re: Samsung 840 & 840 EVO Bug

Wed Oct 29, 2014 7:41 am

The version for non-Windows users is out. They have also apparently updated the Windows version to improve drive detection, for people who had trouble running the version which was released a couple of weeks ago.

From the release notes:
Samsung wrote:
Performance Restoration DOS Version 1.0

Performance Restoration DOS version 1.0 features
- Support Model : Samsung SSD 840 EVO, 840 EVO mSATA
- Firmware Update
- SSD Performance Restoration

Performance Restoration Version 1.1

Performance Restoration version 1.1 features
- Support Model : Samsung SSD 840 EVO, 840 EVO mSATA
- Firmware Update
- SSD Performance Restoration
※ Samsung Performance Restoration v.1.1 does not work, if users did performance restoration through v.1.0

Improvements
1. GUI (Progress bar) improved
2. Improved compatibility of detecting drives with some PC systems

Linkage: http://www.samsung.com/global/business/ ... loads.html (scroll down about halfway for the firmware fix)
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Ninjitsu
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Re: Samsung 840 & 840 EVO Bug

Thu Oct 30, 2014 3:27 pm

Well, here's what I saw on my 1yr, 8 month old 840 SSD, on SATA II:

Without TRIM
Image

Just after the above benchmark, I TRIMed it with Magician and saw:
Image

1.81 TB written, current drive tempis 33*C, although HD Tune couldn't read that for whatever reason.
 
morphine
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Re: Samsung 840 & 840 EVO Bug

Thu Oct 30, 2014 4:55 pm

Samsung has said that there will be an upcoming performance restoration tool for the regular 840 SSDs. Link: click here.
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emphy
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Re: Samsung 840 & 840 EVO Bug

Mon Dec 01, 2014 1:12 am

This bug is also present in some samsung oem drives included in lenovo thinkpads, the restoration software does not support these drives and nothing is said about them. Highly unscientific test: copying 5 GB of data from this June to an sd card took longer than about 10minutes instead of the 1 minute for more recent files. I discovered this when in a hurry :(

Drive (as reported in BIOS): MZ7TE256HMHP-000L7
Model name (from Samsung website): PM851
 
morphine
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Re: Samsung 840 & 840 EVO Bug

Mon Dec 01, 2014 5:10 pm

But you were copying onto an SD card. You're going to be limited by the SD card's speed and the USB interface itself.

Also, copying many small files is absolutely murder for USB pens and SD cards in general.
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The Egg
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Re: Samsung 840 & 840 EVO Bug

Mon Dec 01, 2014 5:42 pm

It's been pretty quiet. Now that some time has passed, I'd be interested to see results on how well the firmware update worked.
 
morphine
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Re: Samsung 840 & 840 EVO Bug

Mon Dec 01, 2014 5:48 pm

The Egg wrote:
It's been pretty quiet. Now that some time has passed, I'd be interested to see results on how well the firmware update worked.

Yours truly will re-test one of these days.
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just brew it!
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Re: Samsung 840 & 840 EVO Bug

Mon Dec 01, 2014 7:41 pm

Mine's had the update applied. I'll test to make sure the bug is fixed at some point.
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emphy
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Re: Samsung 840 & 840 EVO Bug

Tue Dec 02, 2014 1:29 am

morphine wrote:
...You're going to be limited by the SD card's speed and the USB interface itself.
...


5GB in roughly 30 files and yes, I have compared it with copying more recent files to the same card. High speed SD cards are really,really fast nowadays :)
 
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Re: Samsung 840 & 840 EVO Bug

Tue Dec 02, 2014 8:19 pm

emphy wrote:
High speed SD cards are really,really fast nowadays :)

Yeah, that's almost certainly the result of affordable cameras capable of recording HD motion video hitting the market a few years ago. The resulting surge in demand for faster SD cards led to some pretty rapid advancement in that area.

As an aside, I've also discovered that hosting a pair of VMs on a USB3 external SSD results in a much more responsive system than hosting them on an internal HDD. (Yes, I know this is still rather non-optimal; this peculiar state of affairs is a compromise which has resulted from my being temporarily saddled with a less-than-ideal desktop PC at my new job.)
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emphy
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Re: Samsung 840 & 840 EVO Bug

Thu Dec 04, 2014 6:46 am

Interesting, just found a reddit thread with complaints about this OEM drive in the surface pro 3, I am wondering just how widespread this problem is...
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