Why does copying a large file sometimes slow down or fail?

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This is a tough one to solve without having hands on the machine.

First I would check Event Viewer, under Administrative Tools in Control Panel. Always a good first step in troubleshooting a problem. If your hard drive is causing trouble, Windows will log errors there. Other errors may be relevant.

It's probably an application problem of some sort if the hardware checks out. Antivirus, antispyware and/or firewall applications seem to be the most common culprits of system problems.

If you get a specific error message, rather than it just hanging there forever, hit Google for that error. Might find someone else with that problem and a resolution.

I'd dig into it with Process Explorer and Process Monitor, but that's well over the head of the average user.

If I were you, I would see if I need additional memory. Ctrl+Alt+Del and then opening the "Performance" tab will show you available physical memory. If the available memory is LESS than the file you are trying to copy, or less than 75MB, I would into getting more memory.

There are actually two types of memory:
1. physical memory which is your memory stick (fast), and
2. virtual memory, which is on the hard drive (slow).

If your physical memory is full or close to full, windows will automatically "swap" data from your physical memory into a pagefile on your hard drive in order to free up physical space for later applications.

This becomes a problem when you are flipping around multiple applications. Generically, your most frequently used applications (such as those in focus right now) will be moved to the faster physical memory instead of working on the hard drive. Flipping around from application to application will force data to be swapped back and forth multiple times if you do not have enough physical memory to hold everything you are working with at that moment.

Also, performance wise (on systems limited by memory), it may be wise to only allow a single file to be copied at a time. Why? Memory will only need to be allocated to the size of just that specific file, and then cleared for the next file. Multiple MOVE instances will greatly increase the swapping to the hard drive.

Also, generally, it makes no difference if you are moving 1 huge file or multiple small files, as long as you are moving 1 file at a time. Your CPU will only move data to memory on either a byte basis, word basis or long basis, every clock cycle, but it's always the same amount of data at a time; nothing more, nothing less.

For systems that have a lot of free memory, you will see the pagefile is much smaller and the system runs much smoother. It's definitely worth it to get more memory, if you are using a lot.

Also, check to make sure none of your applications are using a massive amount of memory. You can see this in the "Processes" Tab if you arrange by memory usage. > 100MB is a tell that something is wrong unless it's a full screen application/game.

If the copied file is going across a fast ethernet network router, check the NIC to see if its set at Full 100. If it is, try changing to AUTO. If at auto, try setting to FULL 100. One more thing. If you have multiple Spyware tools running, temporarily disable them all and try the copy again to see if that doesn't solve it.

Activities running at background pose a major problems especially if there are many virus guards(vgs) running at the same time. I saw in one laptop, AVG, Norton and AVIRA were actived. I dismissed the other two vgs and defragmented the hd. So everything is fine including downloading large files. One thing to take note, if the softwares were installed by the vendor then the problem already started. It is best to choose which software we need.

One thing you didn't say is what you're copying from and to. If this is happening only when (say) you are downloading from your digital camera to your hard drive, but downloading large files fromm the internet or moving a big file from one directory to another on your hard drive go through just fine, then it's very unlikely that it is a hard disk problem (or a system RAM problem, for that matter). Those sorts of problems would cause *everything* to choke. This is easy to check-- just move a big file on your hard drive, download a couple of big files from different sites on the internet (at different times of the day, if possible), try copying to/from a USB device, etc.

If it's happening with just one (local) device, like your camera, then the first thing I would try would be to update (or reload) the drivers. I'd also check the manufacturer's site for possible firmware upgrades, helper software, etc. for the device, plus possibly a FAQ page to address this issue.

If it's only happening from one web site, then I would suspect that the problem is on their end! Most service providers put bandwidth caps on their hosted sites, and also most sites are sharing resources with other uses-- so a big demand on the server (not just the site itself) could also cause a huge slow-down or apparent jam-up on your computer. The only "solution" in this case is to be very patient (like start it downloading and then go to bed), or to try to download when the site volume will be low.

If it happens from every internet site, but local copies work OK, then I'd look into a problem with your internet service. You could be sharing bandwidth on your internet connection with a surprisingly large chunk of your neighborhood, so if one of them has started doing bandwidth-intensive work when you commonly download your files, that could be a factor. (A friend of mine had this problem, and he found out that a radiologist moved in next door to him and was working from home.) Also, there could be some sort of degradation on your link-- something as simple as water in a J-box could do it; and cables do, eventually, go bad. These are hard to troubleshoot without getting your hands on the hardware, though.

Anyway, hope that helps. Good luck with your problem.

I've also had this problem, particularly when copying large files 100 GB plus. (e.g. server backup files). One thing that really causes problems is if the destination drive is compressed, Windows just doesn't seem to be able to cope and the copy just hangs after a while. The only solution seems to be to buy a bigger destination drive!

Leo's answer is wild pure speculation.

Yes, good thoughts from Leo, but Janet hit the nail on the the head: the biggest piece of missing information is,

"One thing you didn't say is what you're copying from and to."

I, too, kept asking myself, is a network involved? What is on the other side of the network? Is it Vista? What is the speed of
the network? What else is the network doing?
Is any compression involved? Any decryption?

I'm wondering if the reader has multiple computers. If they do, then they can try copying a large file on another computer to find out if the problem exists across multiple computers? If it does, then the issue is most likely with the network or file server. If the issue is limited to one computer, I'd first open up the case and clean out the dust bunnies.

Another issue relevant to the source and destination of the files. If the two are separate partitions of the same physical disk, then the process can slow down significantly due to the movement to and fro of the magnetic head that reads and writes from/to the surface of the disk.
So if the slow-down appears when copying from another partition of the same physical disk but not from one physical disk to another then that is very likely the issue.
Also, keep in mind that when two mediums with different transfer rates are used, the rate is determined by the slowest

"SpinRite" might -- or it might not -- be a great product, BUT I checked out your "SpinRite" link, and quickly found one thing conspicuous by its absence. I'm extremely leery of people who don't put the price of their product up front. Do a text search for a dollar sign (in MSIE, click "Edit" then "Find (on this page)...", then type "$" without the quotes, and click "Find next"). Result? Nada! As soon as I see THAT on the homepage of a product, I quickly go looking for another product. It's like with restaurants -- if you actually have to ASK how much the bill is going to be, you can be sure you can't afford to pay it! :(

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