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

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post #3271 of 3282 (permalink) Old 07-01-2016, 10:48 AM
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Originally Posted by malventano View Post

Ask and you shall receive.

One thing I noted though was that the data-filled 840 sample I had here actually sped up on sequential read passes, meaning it was not as badly affected as the 840 EVO was. The partial recovery reduced the speed gains seen from the firmware update, but they were still apparent. Advanced Performance Optimization capability also helps for extreme cases, or for those who are willing to sacrifice a write to freshen things up.

Thank you very much for the article. Yeah, noticed the improved performance on subsequent reads, too, although I couldn't really tell if it was due to the read itself or because of increasing temps.

Happy to see Samsung releasing a fix for the basic 840. Honestly didn't expect them to. Granted, I had also previously observed the performance deterioration of the 840 wasn't as quick and severe as the 840 EVO. One thing I have to say regarding this, despite the sometimes unbearable speeds, I didn't experience any data loss or corruption on my Samsung SSDs and to me, that is the most important thing (granted, I only compared file checksums).
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post #3272 of 3282 (permalink) Old 07-02-2016, 05:42 PM
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I had a fan blowing across a high performance (unreleased) U.2 SSD what was sitting on the desk here. The 840 was in the same direct path of air flow. It was basically room temperature the entire time.

Let me hazard a guess.... It's from Samsung, it runs hot, and does a couple of GB/s Read and write.


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post #3273 of 3282 (permalink) Old 07-04-2016, 04:39 PM
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Let me hazard a guess.... It's from Samsung, it runs hot, and does a couple of GB/s Read and write.

I wish. This one is from another company. Hopefully Samsung passes me some enterprise samples once I roll out our new test suite.
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post #3274 of 3282 (permalink) Old 07-04-2016, 05:00 PM
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I wish. This one is from another company. Hopefully Samsung passes me some enterprise samples once I roll out our new test suite.

New test suite? Latency percentile wasn't good enough?


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post #3275 of 3282 (permalink) Old 07-04-2016, 05:13 PM
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New test suite? Latency percentile wasn't good enough?

NOT GOOD ENOUGH!

(Sam Breakstone mode disabled)

Latency Percentile was only half of the story. When comparing SSDs with those results, we (everyone) hits an SSD with a saturation load at a specific QD. This means that in the Percentile comparison plots, you have differences in latency *and* IOPS. The reason we haven't posted any enterprise stuff since Latency Percentile was rolled out was that true comparisons can only be made if one of those other differences can be made equal across the tested SSDs. The solution is that I can now apply workloads at a precise paced IOPS and let the SSDs 'float' to whatever QD they need to service those requests. Now the Latency Percentile comparisons will eliminate a variable (IOPS), faster SSDs won't be working as hard, driving their latencies lower, meaning the percentiles can be used for better comparison without having to also account for varying IOPS in the sidebar. The IOPS data that used to be in the legend will be replaced with the average QD of each SSD in the test run.

...so yeah, basically I'm flipping the whole damn thing upside down. We used to have fixed QD that gave max IOPS. I'm doing fixed IOPS and obtaining the variable QD that results (as well as the Latency Percentile at that load). It's the only way I can imagine getting a true a vs. b comparison. It's taken so damn long because I had to do a lot of coding and qualifying tests to get there.
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post #3276 of 3282 (permalink) Old 07-04-2016, 05:33 PM
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Originally Posted by malventano View Post

NOT GOOD ENOUGH!

(Sam Breakstone mode disabled)

Latency Percentile was only half of the story. When comparing SSDs with those results, we (everyone) hits an SSD with a saturation load at a specific QD. This means that in the Percentile comparison plots, you have differences in latency *and* IOPS. The reason we haven't posted any enterprise stuff since Latency Percentile was rolled out was that true comparisons can only be made if one of those other differences can be made equal across the tested SSDs. The solution is that I can now apply workloads at a precise paced IOPS and let the SSDs 'float' to whatever QD they need to service those requests. Now the Latency Percentile comparisons will eliminate a variable (IOPS), faster SSDs won't be working as hard, driving their latencies lower, meaning the percentiles can be used for better comparison without having to also account for varying IOPS in the sidebar. The IOPS data that used to be in the legend will be replaced with the average QD of each SSD in the test run.

...so yeah, basically I'm flipping the whole damn thing upside down. We used to have fixed QD that gave max IOPS. I'm doing fixed IOPS and obtaining the variable QD that results (as well as the Latency Percentile at that load). It's the only way I can imagine getting a true a vs. b comparison. It's taken so damn long because I had to do a lot of coding and qualifying tests to get there.

So, it wasn't anal enough you're going double and triple anal for the nichest of niche reader that needs to know how their SSD performs on an atomic level.

I approve.


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post #3277 of 3282 (permalink) Old 07-04-2016, 07:45 PM
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Quote:
Originally Posted by malventano View Post

NOT GOOD ENOUGH!

(Sam Breakstone mode disabled)

Latency Percentile was only half of the story. When comparing SSDs with those results, we (everyone) hits an SSD with a saturation load at a specific QD. This means that in the Percentile comparison plots, you have differences in latency *and* IOPS. The reason we haven't posted any enterprise stuff since Latency Percentile was rolled out was that true comparisons can only be made if one of those other differences can be made equal across the tested SSDs. The solution is that I can now apply workloads at a precise paced IOPS and let the SSDs 'float' to whatever QD they need to service those requests. Now the Latency Percentile comparisons will eliminate a variable (IOPS), faster SSDs won't be working as hard, driving their latencies lower, meaning the percentiles can be used for better comparison without having to also account for varying IOPS in the sidebar. The IOPS data that used to be in the legend will be replaced with the average QD of each SSD in the test run.

...so yeah, basically I'm flipping the whole damn thing upside down. We used to have fixed QD that gave max IOPS. I'm doing fixed IOPS and obtaining the variable QD that results (as well as the Latency Percentile at that load). It's the only way I can imagine getting a true a vs. b comparison. It's taken so damn long because I had to do a lot of coding and qualifying tests to get there.
Do Windows APIs provide such access when reading data from drives? Or does it have to be somehow workaround and low level accessed without using Windows DLLs? Curious how these SSD testers are made.
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post #3278 of 3282 (permalink) Old 07-04-2016, 08:17 PM
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Do Windows APIs provide such access when reading data from drives? Or does it have to be somehow workaround and low level accessed without using Windows DLLs? Curious how these SSD testers are made.

Everything I'm doing is handled at the application level, relying on standard API calls for all IO. Any other way and it wouldn't be a 'correct' test, as it would bypass the typical path through the NVMe/AHCI driver. In this case, the test app has to be really damn good at pacing the IO's issued, and tracking how long each one of them takes to complete.
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post #3279 of 3282 (permalink) Old 07-04-2016, 08:19 PM
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So, it wasn't anal enough you're going double and triple anal for the nichest of niche reader that needs to know how their SSD performs on an atomic level.

I approve.

What's hilarious about all of this is that the end goal is to *reduce* the number of charts in a review. Sometimes to get the simplest yet most realistic data, you have to jump through all sorts of hoops before distilling down to those very simple results.
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post #3280 of 3282 (permalink) Old 07-08-2016, 10:52 PM
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hi all, new to the forum here and hoping to find some answers for a problem I'm having with the 840 evo. After some research on the net, this thread seems to have the most knowledgeable posters. I bought my 840 evo in 11/2014, which was blazing fast initially until the performance degradation issue hit. I have since then updated to the latest firmware EXT0DB6Q, which subjectively seems to have fixed the problem. However, over time, the computer seems to slow down despite the latest firmware. In 4/25/2016, using the Magician's performance benchmark, my random read/write is 29K/23K and seq read/write in 548/528 I did an advanced performance optimization back then on the Magician software, which restored the random read/write to 90K/50K. Then yesterday, 7/7/16, the computer started slowing down significantly, and a recheck of SSD performance found that random read/write is back down to 29K/23K . I repeated the advanced performance optimization and benchmark found random read/write is back up to 90K/65K. However, the computer seems to have these periodic 0.5 sec freezes here and there which I want to attribute to the evo 840.

Is periodic advanced performance optimization needed every 2-3 months to maintain the optimal performance of the drive? Has that been the experience for other folks who own the 840 evo? Or did I get a bad batch? And are people happy with having to do advanced performance optimization every 2-3 months? Does Samsung consider that fixed?

I'm still under warranty until 11/2017. What has other folks' experience been with warranty service. It seems to me people just get another 840 evo refurb, which I really don't want. Has anyone had success with getting Samsung to give a 850 evo replacement instead?

I'm considering getting a new SSD 480-500Gb capacity. Any recommendations? Do folks pretty much agree with Sean's SSD buyers guide suggestions? It seems like other brands have their own issues as well, but so far I've not read too many problems with Crucial MX200, SanDisk Ultra II, SanDisk Extreme Pro. Has the 850 evo so far been free of the problem that the 840 evo had?

I'd appreciate any comments and suggestions. I'd be interested to hear the competing perspectives of malventano and darkhaze too.

Thanks
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