SSD very slow: it starts fast and then speed drops down

Question

I have noticed a problem on my dell inspiron 13 series 2-in-1 7359.

The SSD is very slow when it has to copy files. It starts very fast (it does 30%-40% of the job) but after 5-6 second the speed drops at 10MB/s. Which I believe is ridiculous for a SSD.

Also the CPU goes up at 100% when I start copying files.

The problem is not only with Ubuntu 16.04 but also with windows 10.

I have a 256GB SSD (SAMSUNG PM871), and I partitioned it in 3 sections:

one EXT4 with Ubuntu 16.04
one NTFS with Windows 10
one NTFS with no operative system

On Windows I installed a Samsung tester tool and it says my write speed is 300-400MB/s, so everything should be fine but of course it isn't.

I have read several pages that talk about similar problems but I can't figure out a solution.

Some link I visited:

My CPU is: Intel® Core™ i7-6500U CPU @ 2.50GHz × 4.

score 2 · Accepted Answer · answered Oct 09 '17 at 20:55

This is normal behavior for SSDs, especially as they get very full. The reason for this is that SSDs need a lot of time to clear up used blocks. They can only write to free blocks. To be fast, they keep free blocks for future use around. This is one of the reasons the TRIM command is important. After the available free blocks are full, the SSD needs to free up more blocks as it writes which makes writing after it ran out of free blocks a lot slower than before.

SSD very slow: it starts fast and then speed drops down

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