Windows 10: Large file copying speed. Why does it slow down?

When I copy a file about 2TB in size from 1 disk to another the speed starts of fast say 185MBps and then drops to about 80MBps. This happens both on my desktop. On my laptop copying between two partitions slows down to a similar speed. Why does this happen?

:)

 

Windows 10 wireless network file transfer speeds is very slow compare to windows 7

These post has so much good information and i also followed these but didn't worked

Copy speed very slow in windows 10

Why are wireless network file transfer speeds soooo slow?

 

N8 internal Mass Memory, inconsistent read/write speed

Hi - yes, I've got plenty of free space on my PC. The same operation targeting my SD Card has no performance issues at all, so the problem isn't at the PC-end. It's only an issue when moving/copying large amounts of data to the internal "Mass Memory" drive,
regardless of source (SD card or PC).



The files being moved were all fairly large, but not like a single 10GB chunk. 1000+ MP3 files typically 5-15 MB of size, and about 50 video clips at around 50 MB each. So RAM on the phone should not be an issue unless one or more of the files completely
depletes available RAM, and even then it shouldn't drop below the Mass Storage write-speed, which I'm assuming is Class 2 or Class 4. (SD card is class 4 btw). I was seeing "Class 0.1" :-/



In any case, RAM depletion / slow write speeds does not explain why phone-access to Mass Memory was horribly slow (listing files) after the copy was done and phone disconnected. The browse slow-down persisted until I rebooted the phone.

 

There is a copy buffer - stuff gets read into memory from the source storage, then written to the target storage, which is checked against the buffer in memory for errors, then the next block of data is read, so at first about 2x the final rate is being transferred, but when the buffer is reading new stuff and checking the last block that has been transferred simultaneously, it has only ~half of the initial rate.

The data copy rate indicator shows the amount of data stored and checked against time - at the end of the operation, it seems to do nothing for a while as data already written to the target is checked against a buffer before the process shuts down.

The reading and writing from memory is the fast part of the operation, but the storage read and write operations are the slowest parts of the operation.

 

Wild guess: the initial, faster speed, reflects system buffering of the write operation.
Once the buffer fills up, the hardware transfer rate is reflected for the rest of the file.

 

Yeah - it is copying to RAM buffer at that speed but can only write to disk at its maximum speed. Once buffer is full, it can only copy as fast as it can write i.e. buffer empties at rate of writing to drive.

That initial burst is an illusion really.

 

Using robocopy built in to windows is the fastest method Anti virus can slow it to a crawl as it will scan on read and write

 

These links may help to understand what is happening :

Enable or Disable Disk Write Caching in Windows 10 - Winaero

Also for Windows 10:

Write-Caching - Enable or Disable - Windows 7 Help Forums


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