How much of a bus width should we be seeing from Sata III?

[SenKa]

Im curious, as I've been seeing near max bandwidth of Sata III recently transferring files from my NVME boot drive to a Crucial MX-500 SSD.

 

Sata III maxes out at a theoretical 600Mb/s, and I am seeing 400Mb/s transferring files. Is this normal, should I be seeing more?

[badreg]

Run CrystalDiskMark. You should be getting 560MBps sequential reads and 510MBps sequential writes.

 

400MBps is within normal for real world performance when overhead is factored in. How large are the file transfers? Once you run out of cache, you would expect a MX500 to slow down to around 300MBps.

[emosun]

while theoretical max speeds exist on paper i dont think i've ever seen anything really hit it's maximum paper limit. whether it be internet or sata or usb or even pci-e slots

[SenKa]

4 minutes ago, badreg said:

Run CrystalDiskMark. You should be getting 560MBps sequential reads and 510MBps sequential writes.

 

400MBps is within normal for real world performance when overhead is factored in. How large are the file transfers? Once you run out of cache, you would expect a MX500 to slow down to around 300MBps.

My test file is ~6GB, drive is currently sitting with 86GB free out of 1TB capacity

[badreg]

3 minutes ago, SenpaiKaplan said:

My test file is ~6GB, drive is currently sitting with 86GB free out of 1TB capacity

 

With a synthetic workload, it looks like you can expect around 475MBps for around 30GB. After that, it throttles between 250 and 425MBps.

 

Again, 400MBps is within normal for real world use, but you can run a synthetic benchmark just to verify.

[mariushm]

Sata 3 is 6 gbps  but for every 8 bits of actual data, 2 bits are used for error correction and other things, so  6 / 10 * 8 = 4.8 gbps or 4 800 000 000 bits per second. There's 8 bits in a byte, so you have 600,000,000 bytes per second.

 

Depending on your units, that's  either :

1. 600 000 KB or 600 MB (divided by 1000)

2. 585 937 KiB or 572.20 MiB/s (divided by 1024, as Windows shows file sizes and transfer speeds)

 

There's some overhead so you can't get 572 MiB/s ... for example, let's say data is transferred in packets of 512 bytes or more, each with a "header" of a few bytes.

But, with big files, you can still get up to around 560 MiB/s, that's the limit.

 

If you want to test your SATA, use some software to create a RAM disk (for example I use ImDisk ) and copy files from your SSD to your computer's memory (the ram drive).

As you test, your maximum speed may be limited by the SSD's write speeds and the amount of time it takes for the SSD to acknowledge that data has arrived correctly inside the drive and that it's ready to receive more data.