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Windows 7: Why does copying files start fast then slow down so dramatically?

11 Dec 2017   #1
martinlest

Windows 7 Home Premium SP1 64-bit
 
 
Why does copying files start fast then slow down so dramatically?

I have a lot of files to move, about 1200GBs to go... The files are more or less all the same size, about 10MBs each. They are being copied from one external HDD to another, via USB3.0 and my Win7 x64 PC.

There are a number of external USB drives involved and they all do roughly the same thing. At first (could be several minutes or even an hour or more) the transfer rate shows as about 30MB/s, at which rate it would be complete in 3-4 hours. But after a while the rate starts to go down, fluctuating between fast and slow, until it can be as little as 1MB/s maximum speed, dipping lower (at which rate the transfer would take weeks).

I could understand if one drive was slow, it may have a fault, but all my USB drives do exactly the same thing. Why is it that a drive capable of moving files at 47MB/s (about the best I get) for some minutes slow down so much? It must be something in Windows 7? If I stop the transfer and reboot, it will set off again at 30-40MB/s.

There is always plenty of free RAM - never less than 12GBs free at the slowest copy speed. i7-4790K CPU @4GHz. Can't see anything obvious in Resource Monitor.. I don't do anything else on the PC whilst the transfer is taking place, as that usually slows down the speed within minutes- I just cut/copy and paste and leave it.

Tried with only system services loading (via ms config), but no change...

Any ideas? Thanks.


My System SpecsSystem Spec
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11 Dec 2017   #2
mrjimphelps

Linux Mint 18.2 xfce 64-bit (VMWare host) / Windows 8.1 Pro 32-bit (VMWare guest)
 
 

My guess as to why the copy operation slows down as it proceeds: when you first start the copy operation, the copy buffer is empty. Therefore, there is plenty of room in the buffer to move the files into. But the buffer then fills up, because the files don't move out of the buffer as fast as they are moving in. At that point you are no longer benefitting from the increased speed of memory; you are limited by the slowest speed in the pipeline, the write speed of your external hard drive.

Here are some ideas for speeding up copying:
http://www.makeuseof.com/tag/4-ways-...er-in-windows/

I've never used either Teracopy or Robocopy, so I can't comment on them. Robocopy comes with Windows 7, and a lot of people swear by it, so I suggest you try doing your copying with Robocopy.
My System SpecsSystem Spec
11 Dec 2017   #3
sml156

Microsoft Windows 7 Ultimate 32-bit 7601
 
 

Believe it or not I find it faster if I have a bunch (1000's or more) of files especially small files to use something like 7zip to compress them then move the compressed file after it's done.

Just recently I had to move about 10000 small files that were less than a Gig altogether and that took longer than moving one compressed file that was over 7 Gig.

Since you are using USB drives unless they are all USB 3 this trick may not work as I stated above.
My System SpecsSystem Spec
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11 Dec 2017   #4
Megahertz07

Windows 7 HP 64
 
 

@mrjimphelps is right. It's the buffer on the External drive that makes it faster at the beginning.
If you're using 2.5" laptop disk on the external enclosure (5400 RPM), the transfer speed is about 15MB/s.
You also have the antivirus that checks every file. If you temporary disable it, the transfers will be higher.
It doesn't matter if you're using a USB 2.0 or 3.X. The bottle neck isn't the USB speed. The bottle neck is the drive.
USB 2.0 = 480 Mb/s = 60 MB/s
USB 3.0 = 5000 Mb/s = 625 MB/s
USB 3.1 = 10000 Mb/s = 1250 MB/s
My System SpecsSystem Spec
11 Dec 2017   #5
martinlest

Windows 7 Home Premium SP1 64-bit
 
 

Thanks for the replies. If the problem is due to the buffer, then perhaps there's nothing to be done? It's very unpredictable - the move has been running at 20-30MB/s for 45 minutes now. Other times, even after a reboot, those relatively fast speeds can only last minutes.

I should have said.. TeraCopy has been my default copy/move application for years. It is not always preferable to Windows native copy, but 95% of the time it works better. Plus it gives a constant readout of the transfer speed (seems mostly accurate when you look at Resource Monitor).

Robocopy is a very good idea - I will try that. I do use it occasionally as it will copy things that no other application will (due to long file names), but had forgotten about it for this copying task. Running from a command line may prove better.

I have thought of compressing - for lots of small files it can be faster, but whatever plagues my PC with copy speeds also affects 7-zip (probably different cause but similar symptom): unzipping files with 7-zip starts fast then slows to a real crawl. WinRar is better. But for all these large files, which do not compress very much anyway, it's not really an improvement. But thanks for the suggestion.
My System SpecsSystem Spec
11 Dec 2017   #6
martinlest

Windows 7 Home Premium SP1 64-bit
 
 

Now copying at c.400kb/s... this is ridiculous.
My System SpecsSystem Spec
11 Dec 2017   #7
SIW2

Microsoft Community Contributor Award Recipient

Vista x64 / 7 X64
 
 

My System SpecsSystem Spec
11 Dec 2017   #8
martinlest

Windows 7 Home Premium SP1 64-bit
 
 

Thanks for the links. (Copy been running OK for almost two hours now. Very unpredictable)...
My System SpecsSystem Spec
12 Dec 2017   #9
Megahertz07

Windows 7 HP 64
 
 

Did you temporary disable the antivirus?
My System SpecsSystem Spec
12 Dec 2017   #10
martinlest

Windows 7 Home Premium SP1 64-bit
 
 

Quote:
Tried with only system services loading (via ms config), but no change...
I assumed that stopped the anti-virus, though I didn't check.
My System SpecsSystem Spec
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 Why does copying files start fast then slow down so dramatically?




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