Solved Why is "time remaining" in copying rearly accurate

[netadict]

well?

 

[barton]

Give About 1 hour remaining for someone smarter to answer

 

[boohbah]

it has something to do with write caching ,
it is fine when it starts then slows down when it has to start flushing to disc.
presumably the calculation is made before the buffer flushing starts

I'm transferring in Windows 7 a movie from my SSD to an external HDD. At first it transfers at like 400MB/s but then slows down and plateaus at 30MB/s. This is hardly abnormal, but I'm just wondering why does it start off so strong and then slow down? It's a single large file. Or is the Windows Explorer transfer speed it displays just inaccurate?

Write caching. Windows will only buffer so much before flushing it to disk so to explorer the first bit seems to fly and then slows down as the buffer has to be written to disk. That's also why you can lose files if you pull it out without ejecting first, although Windows tries to minimize that now by mounting removable media synchronous.

source...

 

[DeaconFrost]

I always thought it was extremely accurate...just that the transfer speeds are never perfectly consistent.

 

[nilank]

That's because reading/writing speeds keep on varying rapidly if there is a mixture big and small files being copied. Copying smaller files takes longer and slow down copying speed whereas it's vice-versa with big files.

Windows calculates the time remaining at regular intervals (maybe a gap of every 2 or 3 seconds), so it seems to vary and is not much accurate since Windows cannot calculate as quick as the speeds change.

Time remaining is more accurate while you are copying large contiguous files, since speeds almost remain constant but is not the case when copying smaller files.

 

[essenbe]

Great answer, Nilank. There is that and a whole lot of factors involved in transfer speed. Also what type of files you are copying. Watch the speed drop when you are copying a text file then go to an ISO file. Sure, an ISO file is usually larger and should take longer, but the transfer speed would remain constant, but it doesn't. I know some people when copying a lot of small files and different file types, put them in 1 folder and zip it up. Then they are copying 1 large file instead of a bunch of small files. I've never tried it, but they say the transfer speed is a lot more constant and faster.

 

[Britton30]

My transfer speed also starts fast and slows to a crawl. Even after it says 100%, it will hang for 20-30 seconds. This is true in my case with compressed or, say, a big >500MB videos file. The window will say Time remaining Calculating.... Never does give a time.

 

[essenbe]

Gary, it's file type as well as size, I think. Video files are a lot harder to copy than other types of files. My guess would be that you get the hang when your disk cache fills up and it can't transfer any more until the receiving disk writes what is in the cache. I'm no expert on this, but that would be my guess. And video files are harder to transfer, just like my ISO files, the speed really drops when copying them. And the end result is, even with a fast SSD, you can only transfer as fast as the receiving disk can write.

 

[Kaktussoft]

Only size matters! And of course if the files are contiguous. And if the disk and computer has to do other things. Filetype doesn't matter. But.... maybe virusscanner scans some filetypes on read or on write.

 

[Britton30]

I have on-access scanning turned off.

 

[kbrady1979]

Just as nilank said, it has to be able to calculate on the fly, based on what the transfer speed is.....which is rarely consistent. Bigger files, of course, will be more consistent and Windows will be able to more accurately calculate time remaining.

 

[netadict]

Thank you alkl for your thoughtful replies