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I was transferring (copying) a huge game file of about 100GB from my laptop to the SATA SSD I already have using the SATA to USB 3.0 (male) connector. Sometimes it does work properly, i.e I do get to see speeds above 300MB/s but many times I see that (including this case) I get about 40MB/s on the same connector, same laptop and the same SATA SSD which is definitely unacceptable for USB 3.0. What happens is as soon as I start transferring something it just stays at 30-35MB/s all the time instead of 300-400MB/s.

I checked this with other laptops as well that supports USB 3.0, but again the same problem, sometimes you do get to see 300-400MB/s but most of the times you just get to see very low transfer speeds.

I want to know what exactly can be the bottlenecking part of this setup or if that's how the USB 3.0 treats the huge files or is there something wrong with my device itself.

System details:

  • Intel core i5-13450HX
  • Zebronics SATA to USB converter
  • WD Green 480GB SATA SSD
Giacomo1968
  • 58,727
Tejas Dahake
  • 153

1 Answers1

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Since the drive is connected through USB, and is behind a USB <> SATA bridge controller, TRIM like command may not reach the SSD.

(See: No TRIM/DISCARD with a SATA SSD connected through an UASP-enabled USB adapter?)

That means that even after file system level deletion as far as the SSD is concerned nothing changed, IOW the LBA blocks occupied by the now deleted files are still considered 'in use'.

These blocks can not be written to until they're erased and only way for the SSD to discover they can be erased (in absence of TRIM) is when these blocks are written to again.

So, a plausible scenario is, that by writing 100 GB to a drive that's 70% full, the SSD runs into a situation where it has not 100 GB worth of erased blocks readily available and that you're waiting for garbage collection to catch up.

Such a situation can easily occur after you tried copying the 100 GB file a couple of times, deleted again, tried again etc.. Since erasing is the slowest of all three NAND operations (read/write/erase) there's a chance that explains low write speeds.