How do you upload the big file in Blob Storage? You use HttpWebRequest to access the Blob Url and convert your file to stream, and give stream variable to HttpWebRequest.GetRequestStream() method? And about "successful upload to less than about 250M, but
over about 250M files are upload faild.", do you ever get any exception messages when request was "failed"? I think if you can provide more details about your problem, it will help us to fix your problem quickly.
An recommended way to upload large files via Blob RESTful service is divede the file to multiple file blocks. For example, you can divede the a large (such as 1000 Mb) file to 20 of 50Mb file blocks and upload all blocks with multiple
web requests. HttpWebrequest will timeout while a long time without any response.