Locked [SSD HELP] WD SN750 vs Intel 660p - Help understanding SSD transfer speeds.

[Dale Martirez]

Hi! I would just like some help understanding how SSD speeds differ from drive to drive... because of this one incident I had encountered just yesterday when extracting files to my SSD.

Usually I extract all my .rar files on my SN750, but I was running out of space so I decided to have the file extracted on my 660p instead until I managed to free up enough space on the SN750.

Both drives are 1TB and the .rar file is roughly 250gb full of just mp4 footage from my client. The 660p is my boot drive (windows 10 drive) and the SN750 is an extra drive that stores games, personal files, documents, etc...

I extracted the 250gb on the 660p and immediately realized that from 8 minutes it tanked to several hours. I monitored the speeds and it was transferring at a rate of 80mb. I cancelled the procedure and decided to restart it. The speeds were fine reading and writing at roughly 300-400mb, until it dips back down to about 80mb and having 100% utilization... this was unacceptable to me...

So I cleared up some space on my SN750, copied the file over, and extracted the contents on the SN750. I was shocked to see the performance difference where the SN750 managed to have speeds of up to 900-1000mb READ and WRITE without it tanking through the whole process. It took roughly 5 minutes for the whole thing to extract!

Can someone help me understand why this is? I tried doing my own research but I end up finding more questions than answers and that looking at the tech specs of these SSDs make me feel even more dumb... so I appreciate any help from the more informed.

Feel free to leave me questions so that I can provide any further details needed to properly find out what is going on here...

Thank you in advance!

Edit: Thank you for moving my post to the proper forum... sorry for placing it in the wrong forum initially!

 

[Baronstragen]

Well, reviewing the specifications on both drives your Intel SSD is roughly half the speed of your WD. Not only that but your Intel is your boot drive, so has processes running in the background. Basically your Intel is the slower one. For booting up OS, it doesn't matter as the speed difference would be very very slight. It's better to have your WD as your storage/game drive because not only will it be faster to run games and do file transfers/extractions, but it's also free of background running processes. Also, the NAND memory differs. Basically the memory is layered to allow for greater optimization and throughput rate in the WD drive. I'll skip the rest of the technical nuances.

 

[Cyler]

Welcome to the technology industry where everyone is saying the "truth" about their products... but everybody lies.

The subject you opened is a big one and will take several posts to cover so I will just give some not extremely technical info and will try to keep it simple for most to be able to read and understand and whoever wants will have to do further research on the web. In that effort, I will oversimplify some things so keep that in mind.

Problem No1: SSD Technology and Cells
Long story short, SSDs (including NVMe) as a disk are made out of cells. When we store one bit per cell it's called Single Level Cell (SLC) if we store 2 we called it Double or DLC, if we store 3 we call it triple or TLC, and at 4 bits we call it quad or QLC. Here is the catch. SLC can be 4 times as fast as QLC, QLC stores 4 times as much data as SLC. Why is that an issue tho? What some manufactures do is split the disk in 2 (the % is different for each manufactured) and use part of the disk as SLC (for speed) and the rest as QLC for storage. So when you write a file it uses the SLC part, and when you don't use the file anymore, the controller transfers it to the much slower QLC part in the background. As you fill the disk, of course, the SLC portion that is used gets smaller over time which makes the disks lose speed as they get fuller.

A small example, let's say you have 1 TB disk and 10% is used in SLC mode. that is 100 GB. When your disk is half full (500 GB), the slc portion will drop to 50GBytes. and so on. Now if you read/write a file that is 100 GB... A part of the process will be very fast since it uses the SLC portion and when it hits the limits... It switches to QLC and we observe the speed decrease. Sounds familiar?

Problem No2: DDR cache
Cache. Each disk has a DDR ram cache internally. Whatever is written to that cache goes bLazing fast. When the cache is full... speed slows down. Needless to say that each disk has different sizes of cache and so, different performance.

Problem No 3: technology used.
Tho 2 disks can NVMe doesn't mean they are the same or even at close speed. It's like saying since Fiat and Ferrari are both cars, they can both run at the same speeds... Memory types used, stacking technology, and even the type of controller can affect performance and that's why you see variations in both speeds and prices. SSDs also have use cases. Some are better to be used for Disk cashing, others for general use, etc.

Now your problem is actually a factor of all 3 of the above.
Different technologies and controllers on each disk, Cache running out, disks not equally loaded, etc can lead to performance degradation and variation.

Hope it helped.

 

[Dale Martirez]

Well, reviewing the specifications on both drives your Intel SSD is roughly half the speed of your WD. Not only that but your Intel is your boot drive, so has processes running in the background. Basically your Intel is the slower one. For booting up OS, it doesn't matter as the speed difference would be very very slight. It's better to have your WD as your storage/game drive because not only will it be faster to run games and do file transfers/extractions, but it's also free of background running processes. Also, the NAND memory differs. Basically the memory is layered to allow for greater optimization and throughput rate in the WD drive. I'll skip the rest of the technical nuances.

Thanks so much for this response! I'll look into these more in the morning Appreciate it!

 

[Dale Martirez]

Welcome to the technology industry where everyone is saying the "truth" about their products... but everybody lies.

The subject you opened is a big one and will take several posts to cover so I will just give some not extremely technical info and will try to keep it simple for most to be able to read and understand and whoever wants will have to do further research on the web. In that effort, I will oversimplify some things so keep that in mind.

Problem No1: SSD Technology and Cells
Long story short, SSDs (including NVMe) as a disk are made out of cells. When we store one bit per cell it's called Single Level Cell (SLC) if we store 2 we called it Double or DLC, if we store 3 we call it triple or TLC, and at 4 bits we call it quad or QLC. Here is the catch. SLC can be 4 times as fast as QLC, QLC stores 4 times as much data as SLC. Why is that an issue tho? What some manufactures do is split the disk in 2 (the % is different for each manufactured) and use part of the disk as SLC (for speed) and the rest as QLC for storage. So when you write a file it uses the SLC part, and when you don't use the file anymore, the controller transfers it to the much slower QLC part in the background. As you fill the disk, of course, the SLC portion that is used gets smaller over time which makes the disks lose speed as they get fuller.

A small example, let's say you have 1 TB disk and 10% is used in SLC mode. that is 100 GB. When your disk is half full (500 GB), the slc portion will drop to 50GBytes. and so on. Now if you read/write a file that is 100 GB... A part of the process will be very fast since it uses the SLC portion and when it hits the limits... It switches to QLC and we observe the speed decrease. Sounds familiar?

Problem No2: DDR cache
Cache. Each disk has a DDR ram cache internally. Whatever is written to that cache goes bLazing fast. When the cache is full... speed slows down. Needless to say that each disk has different sizes of cache and so, different performance.

Problem No 3: technology used.
Tho 2 disks can NVMe doesn't mean they are the same or even at close speed. It's like saying since Fiat and Ferrari are both cars, they can both run at the same speeds... Memory types used, stacking technology, and even the type of controller can affect performance and that's why you see variations in both speeds and prices. SSDs also have use cases. Some are better to be used for Disk cashing, others for general use, etc.

Now your problem is actually a factor of all 3 of the above.
Different technologies and controllers on each disk, Cache running out, disks not equally loaded, etc can lead to performance degradation and variation.

Hope it helped.

Very informative but super easy for me to absorb. I completely understand what you mean from your examples and it's definitely enough for me to work with in order to understand why these speeds are what I am getting.

I would like to request this thread to be closed/solved for I am now more informed as to what may have caused these results in my rar decompression.

Thank you again @Cyler