Slow SSD Write speeds

[JohnCoool]

Over the past 1-2 months I have been trying to find out why I am not getting good write speeds.

 

I have a thread open about this in With Samsung but no one seems to know either.

 

I upgraded two old laptops. One has a SATA II and the other has SATA III interface.

 

All benchmark tests show good results.

 

I am copying files from my HD that is on the HD caddy. One of them is SSHD and the is 7200RPM HD.

 

I had two cheaper type of SSD but did not give good write speeds so decided to buy 2double size SSD from Samsung at 500GB. I enabled DRAM and got Write speeds on one up to 1GB and the other over 2GB but only in Benchmark test.

Real test From HD to SSD is between 5-50MB/s.

From SSD to HD is over 100MB/s.

 

The faster speed image is the SSD to HD 7200RPM.

 

Any idea what is going on?

 

 

 

[mariushm]

The reading speed from a mechanical drive will vary, depending on where the data is located and how fragmented it is.

You can use a tool like HD Tune -  https://www.hdtune.com/ -  to determine how fast a mechanical drive reads data , it shows a picture that looks like this :

 

So for example, with the 750 GB drive above, if your file is NOT fragmented and positioned right at the start of the drive, you would read the file from this drive at 90 MB/s (the blue graph) ... but if the file is physically located towards the other edge of the drive you would read files at as low as 50 MB/s

If the file is fragmented in multiple pieces, the drive has to seek (move the read/write heads) from one area of the drive to somewhere else .. so it may copy 20% of the file at 90 MB/s because that chunk of the file is at the outer edge of the drive, then go down to maybe 60 MB/s for the other chunk that's closer to the other side.

The copy transfer will also be slow if you have a lot of small files, because the hard drive has to constantly read the metadata (where the file is located) and then seek (move the heads to where file is) and start reading it.

 

If you want to truly test the write speed of the SSD, create a ram disk using a tool like ImDisk for example (open source), copy a few GB into ram, then copy that data to the SSD, and it should be copied very fast.

 

About SSDs ,,, some can't sustain the maximum write speed for unlimited time. A lot of cheap drives keep a portion of the free flash memory in a special mode called pseudo-slc which can be written much faster and has higher endurance and use this area to cache writes. Once you're done copying something, the SSD in background slowly transfers the data from this cache area to the more permanent location.

 

Some drives only have a small amount of such pseudo-slc write cache, for example let's say 10 GB.  So for example, you may start copying a 50 GB file to the SSD and you copy the first 10 GB at around 400-500 MB/s from another SSD or from a NAS (if you have a 10gbps connection) and then as you filled that write cache, the sata SSD slows down to maybe 200-300 MB/s, even less (for example around 100 MB/s for SSDs that use QLC memory chips)

 

You say you enabled DRAM... You probably mean some software ram caching, and I suspect what you say about RAM on the Samsung drive is a trick where some part of RAM in your computer is used to cache writes and tell you the transfer is done before the data is actually written to the SSD... the idea is that after the copy window tells you the job's done, the Samsung driver can keep writing the data to SSD in background.

 

[JohnCoool]

The DRAM is an option that comes with the SAMSUNG SSD software to enable it. Gets enabled with a feature called RAPID mode.

 

I am not sure if it works with RAM or it is a chip on the SSD but either way I am not getting any improvement in the performance.

 

The explanation that you gave me is like a software that I tried before called Primocache but also did not work for me on the SATA II laptop. Did not seem to work any different than normal.

 

On the SATA III interface laptop. I am getting 450 MB/s writing from SSD to RAM drive (2 files that are 1.37GB in size). Writing the same two files back from RAM to SSD goes only from 5-50MB/s

 

On the SATA II interface laptop. I am getting 140 MB/s writing from SSD to RAM drive (1 file that is 2.41GB in size). Writing the same file back from RAM to SSD goes only from 5-30MB/s

 

The below link describes RAPID mode in detail.

 

https://semiconductor.samsung.com/resources/white-paper/Samsung_SSD_Rapid_Mode_Whitepaper_EN.pdf

 

 

[NAME NOT AVAILABLE]

What version of windows are you running?

 

[JohnCoool]

Nevermind!

 

I found the cause of the slow performance.

 

I keep my partition on compressed from properties. I guess it was compressing the files while writing them.

 

Once I removed it and restarted all went back to normal.

 

Had to process the the uncompressed files for C.

 

Usually this process causes up to 50% defragmentation.