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PRB: Cannot Upload Large Files When You Use the HtmlInputFile Server Control
Article ID: 295626 - View products that this article applies to.
This article was previously published under Q295626
When you try to use the HtmlInputFile control to upload a large file, the file may not be uploaded.
This problem occurs because the default value for the maxRequestLength parameter in the <httpRuntime> section of the Machine.config file is 4096 (4 megabytes). As a result, files that are larger than this value are not uploaded by default.
To resolve this problem, use one of the following methods:
By default, this value is restricted to 4 MB to restrict possible Denial of Service attacks.
When the maxRequestLength attribute is set in the Machine.config file and then a request is posted (for example, a file upload) that exceeds the value of maxRequestLength, a custom error page cannot be displayed. Instead, Microsoft Internet Explorer will display a "Cannot find server or DNS" error message.
Theoretically, the maximum file upload size is fairly large. However, because of ASP.NET health monitoring, you cannot upload very large files in ASP.NET. The ASP.NET worker process has a virtual address space of 2 gigabytes (GB). However, the ASP.NET worker process only uses a little more than 1 GB because of health monitoring and memory fragmentation.
During the upload process, ASP.NET loads the whole file in memory before the user can save the file to the disk. Therefore, the process may recycle because of the memoryLimit attribute of the processModel tag in the Machine.config file. The memoryLimit attribute specifies the percentage of physical memory that the ASP.NET worker process can exhaust before the process is automatically recycled. Recycling prevents memory leaks from causing ASP.NET to crash or to stop responding.
Additionally, other factors play a role in the maximum file size that can be uploaded. These factors include available memory, available hard disk space, processor speed, and current network traffic. With regular traffic of files being uploaded, Microsoft recommends that you use a maximum file size in the range of 10 to 20 megabytes (MB). If you rarely upload files, the maximum file size may be 100 MB.
Note You can upload files that are larger than 100 MB in ASP.NET. However, Microsoft recommends that you follow the maximum file upload sizes that are mentioned in this article. To determine more precise file sizes, perform stress testing on computers that are similar to the ones that will be used in production.
You may notice the following error messages if you encounter file size limits during the file upload process: