Why does the speed decrease while copying from an external harddrive?

windows-7 external-hard-drive file-transfer

25,771

OS and drive buffers have filled up/been exhausted, and now you're transfering data as fast as the hard drive can supply/consume it.

25,771

Svish

Software Developer, Geek, HSP, SDA, ..., open, honest, careful, perfectionist, ... Currently into indoor rowing and rock climbing, just to mention something non-computer-related... Not the best at bragging about myself... so... not sure what more to write... 🤔

Updated on September 17, 2022

Comments

Svish almost 2 years

I have an external hard drive that I needed to copy about 30 GB from. 8 DVD image files. The copy started out at 160 MB/s, quickly went down to around 80 MB/s and then slowly during the process it has now gone down to 11 MB/s (2.7 GB left)... What is going on here? Why does this happen?

Using Windows 7, copying from an NTFS formatted USB drive, SAMSUNG HM160HI USB Device. As far as I know it is connected to a USB 2.0 (otherwise I think Windows would have complained?) and it is platters, not solid state.

I'm getting the transfer speeds from the regular Win7 copying dialog (after clicking the Show Details button)
- Joe_Rose almost 14 years
  
  Is this a USB drive? Is it in a USB 2.0 port? Is it solid state or platters? Where are you getting the transfer speeds from?
- Zaz over 13 years
  
  I've recently been moving large amounts of data around and, upon investigation, found this effect everywhere. It had me completely stumped.
- sancho.s ReinstateMonicaCellio about 9 years
  
  There is a later question superuser.com/questions/383741/…, so the other would be a dupe (but it may be worth checking the answer).
Joe_Rose almost 14 years

+1 - It's also possible the initial estimates were inaccurate, or that there was compression coming in to play that's not applicable on the whole drive.
Svish almost 14 years

Is there a program or something I can use to measure where the bottle neck is? Not extremely important, but would just be interesting to see if it's my system or the drive or the connection or what it is.
Svish almost 14 years

But is it the internal or the external ones that are likely to be the "problem"? Or do they work the same way and are there for equally "at fault"?
Zaz over 13 years

@Svish: Internal and external hard drives are the same thing; if you wish to remove the bottleneck you should look into SSDs or RAID arrays.
Svish over 13 years

@Josh: Ok, so it has to do with the hard drive itself (Single vs Raid vs SSD), not the connection (USB vs SATA)
Zaz over 13 years

@Savish: The system as a whole can only go as fast as the slowest part. A USB cable is usually slower than a hard drive, so will limit data transfer speed.