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:
- In the Machine.config file, change the maxRequestLength attribute of the <httpRuntime> configuration section to a larger value. This change affects the whole computer.
- In the Web.config file, override the value of maxRequestLength for the application. For example, the following entry in Web.config allows files that are less than or equal to 8 megabytes (MB) to be uploaded:
<httpRuntime maxRequestLength="8192" />
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
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
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.
You can upload files that are larger than 100 MB
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:
You may also find
that uploads occur very slowly. If you watch
the Aspnet_wp.exe process in Windows Task Manager, you will notice that the
memory delta changes by 64 KB every 1 to 2 seconds. Depending on the size of
the file, this delay may cause the ASP.NET worker process to recycle because of
a responseDeadlock error.