External SSD slows down during prolonged writes

[DarkEnergy]

I notice that my external Samsung 840 EVO slows down write speeds during data transfer after awhile. It's not related to Windows temporarily storing data into memory either and it's also not related to the SSD enclosure (as far as I can tell, but it's possible). Transferring a 10gb 7zip file, write speeds start at around 100 mb/s and after about 1/3 of the way slow down to shitty 20mb/s for the entire rest of the transfer. As a comparison, I tried it with a sandisk extreme flash drive, which was able to transfer all of it while maintaining around 90mb/s. In other words, my flash drive is WAY faster during prolonged writes than my SSD. The SSD has over 80gb of free space, and transfers over USB 3.0 (or 3.1, not sure). 

The 840 EVO is formatted as NTFS while the sandisk is formatted as exFAT.

An interesting side note, my main OS in on the same type of SSD, 840 EVO but is an older model. Transferring the same file below, to the OS SSD, it maintains 247mb/s the entire transfer. (400mb/s+ buffer to system memory which I exclude).

 

Windows 10 with latest updates, drivers are up to date.

 

Here is transferring to the 840 EVO (10gb file)

 

Comparison, transferring to the sandisk extreme flash drive

 

CrystalDiskMark for a 2gb transfer to the 840 EVO and then the 16gb (prolonged) transfer comparison

 

As comparison, here's the sandisk extreme flash drive speed from CrystalDiskMark, with both 2gb and 16gb runs. 

 

My only thought, after some research involves Samsung's TurboWrite feature. According to Anandtech, the 250gb varient of the 840 EVO has a buffer size of 3gb. Comparing to my first screenshot of file explorer transfer speeds, it would appear that the slow down happens around the 3gb mark. That said, why would it slow down to around 15gb/s speeds? And why doesn't it do the same to my OS SSD (also an 840 EVO)? I don't know what or if the sandisk extreme flash drive has a buffer size, but it never slowed down transferring the 10gb file. 

https://www.anandtech.com/show/7173/samsung-ssd-840-evo-review-120gb-250gb-500gb-750gb-1tb-models-tested/4

 

 

 

[Electronics Wizardy]

have you done a firmware update on the drive? I remember the 840 evo having some issues.

[DarkEnergy]

13 minutes ago, Electronics Wizardy said:

have you done a firmware update on the drive? I remember the 840 evo having some issues.

Took awhile to figure out, apparently Samsung Magician doesn't detect drives when they're external. After plugging it into a sata interface, it shows it as having the lastest firmware. 

[Electronics Wizardy]

5 minutes ago, DarkEnergy said:

Took awhile to figure out, apparently Samsung Magician doesn't detect drives when they're external. After plugging it into a sata interface, it shows it as having the lastest firmware. 

Do you get the same speed dropoff when its a internal drive?

[DarkEnergy]

With that external SSD connected to sata (now internal), the issue isn't as extreme. SSD to SSD (the one that used to be external) transfers over 200mb/s for most of the copy but too, drops down to around 30mb/s eventually making it overall slower than the sandisk flash drive. Transferring the data like I did in the tests however, it writes at 127mb/s the entire time with the HDD being the bottleneck (HDD was being READ from in tests). This leads to something interesting, being that even though SSD to SSD (the one that used to be external) starts out very fast, in the end, transferring from HDD to SSD (the one that used to be external) is faster. This is because SSD to SSD ends up dropping transfer rates to incredibly slow. Quite confusing. 

 

@Electronics Wizardy

[Lady Fitzgerald]

How much free space does the external SSD have?

[DarkEnergy]

 

1 minute ago, Lady Fitzgerald said:

How much free space does the external SSD have?

35 minutes ago, DarkEnergy said:

The SSD has over 80gb of free space,

I know, it's quite the block of text to sift through, it got more complicated as I wrote it.