<p>My ASP.NET application allows users to upload and download large files. Both procedures involve reading and writing filestreams. What should I do to ensure the application doesn't hang or crash when it handles a large file? Should the file operations be handled on a worker thread for example?</p>

Make sure you properly buffer the files so that they don't take inordinate amounts of memory in the system.
e.g. excerpt from a download application, inside the while loop that reads the file:
```
```
// Read the data in buffer.
length = iStream.Read(buffer, 0, bufferSize);

// Write the data to the current output stream.
Response.OutputStream.Write(buffer, 0, length);
```
```
Where bufferSize is something reasonable, e.g. 100000 bytes, the trade-off is that it will be slower for smaller buffer sizes.
http://support.microsoft.com/kb/812406
Edit: Also be sure that IIS is set to take a large enough
request length
(IIS7) and timeout.