The M.2 interface brings PCI-Express to a tiny form factor that works well with notebooks and mini computers like the Lini 1S.
Our customers were already asking about the 950 Pro before it was released and we got a couple of them for testing as soon as we could.
Based on other reviews of the 950 Pro we expected thermal throttling to be an issue with the drive and we were prepared to develop a custom cooling solution if the need arose.
Samsung 950 Pro Overview
Samsung 950 Pro Retail Box
Samsung 950 Pro Bare Drive
With the sticker removed you can see the Samsung UBX controller chip on the far left. The small chip to the right of that is the RAM cache and the two chips on the far right are the VNAND.
On the ASRock Gaming-ITX/ac motherboard used in the Lini 1S the M.2 slot is underneath the motherboard and has a full 4X PCI-E 3.0 lanes available for it, so the drive is will not be bottlenecked by the interface.
The official specs for the 512GB 950 Pro list a 2500MB/s max sequential read and 1500MB/s max sequential write. These numbers make the 950 Pro the fastest consumer oriented SSD on the market, besting the Intel 750 series.
Unlike the Intel 750 the Samsung 950 pro does not have a beefy heatsink attached to it. It stands to reason that even if Samsung's implementation is vastly more efficient than Intel's heat will be a problem.
Samsung 950 Pro CrystalDiskMark
The 950 Pro nails its advertised maximum speeds when running at a queue depth of 32 in sequential workloads and comes close in straight sequential performance.
Queue depth refers to the number of reads or writes that are attempted to be performed simultaneously.
The Samsung UBX controller in the 950 Pro is an 8 channel device so it can perform operations across 8 different memory chips simultaneously. This allows a single 950 Pro to act like a RAID array with 8 drives attached to it.
Since the 950 Pro only has two VNAND chips, each containing 48 stacked layers, it can be assumed that each channel of the UBX controller is addressing some segment of the layers within one of the chips.
The multi-channel nature of SSDs allows them to perform better in sequential work loads than in random workloads because a sequential file can be "striped" across all of the drive's memory controllers and spread out across different memory chips.
Because there is latency every step of the way from the CPU, to the system RAM, to the SSD controller, to the SSD's RAM cache, to the VNAND, it is possible to achieve higher throughput overall by stuffing more requests into the channel. Each request can only be performed so fast due to the round trip latency but having requests stacked up at the SSD controller and waiting as soon as it is available allows the SSD to run at full capacity all the time, so upping the queue depth helps to achieve maximum rates.
Samsung 950 Pro AS SSD
In real world desktop use it is rare to see high amounts of concurrent IO requests so the 0 queue depth numbers ("Seq" and "4K") are more realistic.
The 4K random read number looks really bad compared to the Seq number.
This number reflects the true latency of the controller and the VNAND. Each random request has to go all the way through the many layers of components in the system.
The difference between 4K random and sequential performance at 0 queue depth is likely explained by the Samsung UBX controller performing some read ahead caching where when a request for one piece of data from a file is made then the data after that is also read and stored in the onboard RAM cache which allows it to be retrieved much more quickly if it is requested next.
Samsung 950 Pro ATTO Disk Benchmark
With the ATTO Disk Benchmark running the longest possible test with a total write length of 32GB and a queue depth of 10 it is possible to clearly demonstrate the effect of thermal throttling on the Samsung 950 Pro.
Once the amounts of sequential data reach 32KB the drive is able to hit its maximum performance of 2500MB/s read and 1500MB/s write.
However, as the test progresses, these numbers start to tail off, and in the end the drive has fallen down to around 1700MB/s read and 1100MB/s write.
If you look the AIDA64 Extreme sensor output on the left you can see that the drive is reporting a temperature of 74C, which would make it appear that the thermal threshold for the device is around 75C.
Thermal Throttling Solved
With the thermal throttling issue identified we went to work on figuring out how to solve it.
Measuring 950 Pro Under Load with Infrared Thermometer
The first step to developing a thermal solution is information gathering. Besides looking at benchmark results and hardware monitors we also got out an infrared thermometer to measure heat on different parts of the Samsung 950 Pro.
Using the infrared thermometer we were able to determine that the Samsung UBX controller is the chip that gets the hottest, which we expected, and the RAM and VNAND do not seem to have any thermal issues of their own.
One of the advantages of the Lini PC case is that it is solid aluminium which means that it can serve as a giant heat sink.
All that is needed is to conduct the heat from the Samsung 950 Pro, conveniently mounted underneath the motherboard, to the case beneath it.
Samsung 950 Pro with Copper Shims
Arctic Thermal Pad
Arctic Thermal Pad on Samsung 950 Pro
Finally to achieve a good thermal interface between the copper shims and the Lini PC aluminium case we used a piece of Arctic Thermal Pad material.
With the thermal solution in place we seated the motherboard back onto the bottom of the case and screwed it down for another round of testing.
Samsung 950 Pro Lini 1S Custom Thermal Solution
Lini 1S Custom Thermal Solution ATTO Disk Benchmark
With the Lini PC custom thermal solution in place on the Lini 1S with a 512GB Samsung 950 Pro it is possible to see this drive running at 100% capacity across the board.
Unlike the first run of the ATTO Disk Benchmark this time transfer rates never drop beneath their 2500MB/s read and 1500MB/s maximums.
Looking at AIDA64 the drive is now reporting a temperature of only 47C at the end of the run as opposed to being thermally throttled at 74C.
With our custom thermal solution we were able to reduce peak operating temperatures by 37% and keep the drive running at full speed while at a comfortable 47 degrees Celsius.
Whether you want to get maximum performance or you just want to extend the life of your drive and your system by maintaining low operating temperatures a custom thermal solution is definitely recommended when deploying the Samsung 950 Pro.
At Lini PC every Lini 1S with the Samsung 950 Pro that we ship comes with our custom thermal solution installed and fully tested to verify that it is operating as expected.
Once again we are excited to be bringing the latest high performance technology to market and we are even more excited to have the thermal throttling issues with this drive completely solved.