Samsung 840 EVO read speed drops on old-written data in the drive - Overclock.net - An Overclocking Community

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Samsung 840 EVO read speed drops on old-written data in the drive

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post #1 of 3282 (permalink) Old 08-16-2014, 04:53 AM - Thread Starter
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Edit by Sean Webster:

Thanks to everyone who has posted in this thread and spread the word on the matter, Samsung has taken note of the Samsung Evo Series SSDs degrading performance of older data. A firmware fix for the issue is scheduled to be released October 15th.

Furthermore, I would like to personally thank Techie007 and BrainSplatter for their developing of benchmark software to verify this issue.

Their latest testing software is located here: https://www.overclock.net/t/1512915/read-speeds-dropping-dramatically-on-older-files-benchmarks-needed-to-confirm-affected-ssds

Hi to all!
In my system I have 3 Samsung SSD drives:
1: 256 840 PRO with Windows 7 OS and programs
2: 500GB 840 EVO
3: 1TB 840 EVO

Both EVO drives have the same exact problem, read speed on old files drops with time as low as ~60Mb/sec. New written files instead are as fast as advertised read/write speed ~450Mb/sec and so if I start a new benchmark with any benchmarking app.
Please note that the data must be "old" in terms of weeks or months to show the problem. Newly-written data read speed is fast as advertised, this is why benckmarks shows always a fast drive..

After a reboot the read speed improves a bit, but not much (as also reported in another thread, don't remember where) and after some "on" time return to the pre-reboot speed.

This seems to me a common hardware problem of those cheap SSD...
Anyone with those SSD with old data on it, may do some read speed test?

One good test for this is using the good old HDTach v3 program. It will show very well the drop on read speed on disk zones where old data is, using the "long bench" option. It works very well on windows 7 in XP compatibility mode.

This seems to me a serious problem on these disks. I have also a 256 840 PRO which does not have the problem (same PC and all SSD connected to INTEL AHCI ports, well configured).

To illustrate, here is a HDTach bitmap of my 500 EVO, where the last part is "free" space:


And to compare, here is my 840 PRO, same pc, same AHCI Intel ports:


And as I said, posting a new benchmark is useless as it will be exactly as advertised... The problem is reading old data and it gets worse over time.
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post #2 of 3282 (permalink) Old 08-19-2014, 04:36 AM
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Interesting. Can u post your S.M.A.R.T. data? There is a theory that it might be related to a sudden loss of power and the following 'power recovery' procedure:

ID # 235 Power Recovery Count:
http://www.samsung.com/global/business/semiconductor/minisite/SSD/us/html/about/whitepaper07.html

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post #3 of 3282 (permalink) Old 08-19-2014, 04:48 AM
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subbed , this is an interesting investigation, will have a go at benching if I get time.

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post #4 of 3282 (permalink) Old 08-19-2014, 05:35 AM
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I have now seen several reports of this problem on different sites. I own a 1TB EVO since a few days and will try to verify this problem although it supposedly affects 'old' files. But 'old' in all likelihood doesn't mean that you have to leave your SSD lying around for 1 year and then the read data rate even on big 'sequential' files will have dropped significantly. It might rather be related to writing a lot of files or some infrequent event like a sudden system power loss (reset, blue screen, ...).

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post #5 of 3282 (permalink) Old 08-19-2014, 05:50 AM
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Very interested to hear what comes of this. I was just debating picking up a 1TB Evo personally.
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post #6 of 3282 (permalink) Old 08-19-2014, 05:52 AM
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Quote:
Originally Posted by Booty Warrior View Post

Very interested to hear what comes of this. I was just debating picking up a 1TB Evo personally.

I think the argument for picking up an Evo is still very valid, the performance gains are insane.
Of course many users still use slow drives for data that's not frequently accessed, which may be something to factor in.

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post #7 of 3282 (permalink) Old 08-19-2014, 06:00 AM
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from your print screens i didn't see any old vs new data speed change, so that's probably an illusion of yours.

All i could see is that the free space of your ssd has higher read speeds, so check if your trim is enabled.

also hd tach is pretty much outdated and created for hdds.

use newer benchmark software
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post #8 of 3282 (permalink) Old 08-19-2014, 08:12 AM
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Quote:
Originally Posted by Eddie Obscurant View Post

also hd tach is pretty much outdated and created for hdds.

use newer benchmark software

This is true but as I have seen in other similar reports, the problem was usually noticed when people copied big 'old' files and noticed that the performace was much worse than it should be.

The easiest test would be to find an old big file (multiple gigabytes if possible) and copy it to another fast SSD. If performance is much lower than 300MB/s then there is something wrong.

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post #9 of 3282 (permalink) Old 08-19-2014, 10:34 AM - Thread Starter
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Quote:
Originally Posted by BrainSplatter View Post

This is true but as I have seen in other similar reports, the problem was usually noticed when people copied big 'old' files and noticed that the performace was much worse than it should be.

The easiest test would be to find an old big file (multiple gigabytes if possible) and copy it to another fast SSD. If performance is much lower than 300MB/s then there is something wrong.

This is exactly how I saw the problem the first time. I moved a big file (virtual machine disk file) from the EVO drive to the 840 PRO and the copy speed was less than 100MB/sec. Did the opposite and the speed was ~500MB/sec.

After that I did a lot of tests with new and "old-written" files and I'm pretty sure of the problem.
To better explain to you, I'll repeat a test I already did to investigate the problem:
I'll move some big files (two complete VMs) from the EVO to the PRO and back, testing the EVO drive with HDTach before, without the files (after trim) and with the files copied back.
This time the file copy speed ranged from 150MB/sec to 260MB/sec from EVO 500GB to the SSD 840 PRO 256 (~100GB total). Copying the files back to the EVO was very fast as expected: 400-450MB/sec.
Here are HDTach measurements:
Before:
qDwZh7V.png
Without files (after some trim time):
ByeGWBy.png
Files back to it:
6yT7ZdB.png

@Eddie Obscurant: trim affects writing performance (a not-trimmed drive need first to clear memory cells before writing new data) not reading speed. Anyway in my system is working OK, otherwise also the PRO drive will be affected but that's not the case.
To show the problem we need a benchmark program that reads existing data from the drive. Most SSD benchmarks write and than read new files for benchmarking and the speed will be at max!
May you suggest a newer benchmark program that measure read speed of exisiting data? I'll gladly execute that.

Finally that's a SMART of the drive:
2r5RBaX.png
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post #10 of 3282 (permalink) Old 08-19-2014, 10:48 AM - Thread Starter
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Quote:
Originally Posted by BrainSplatter View Post

Interesting. Can u post your S.M.A.R.T. data? There is a theory that it might be related to a sudden loss of power and the following 'power recovery' procedure:

ID # 235 Power Recovery Count:
http://www.samsung.com/global/business/semiconductor/minisite/SSD/us/html/about/whitepaper07.html

About that theory... May you point me to these discussions?

My system currently in under UPS and it's many months it did not have a power loss or a BSOD. Only normal shutdowns/restarts, but usually it's on 24/7.
BUT after I bought the EVO drive I did some experiments "on the fly" with it by connecting and disconnecting it as external drive and this may have raised that counter. But after these tests, I reformatted it and put it online.

Maybe I should check if a normal shutdown on my system will raise that number, though.
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