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Page blobs can be up to 1 TB, which cannot be represented with an int (which can represent a max value of 2GB). Thus, the length parameter should be a long, which can represent up to 9ZB (which should be enough for anyone. :-))
Interestingly, createBlobPages does take a long parameter.
After this is fixed in the service layer, this bug should be reassigned to the Storage team for fix in the client layer.
There is already an issue tracking the seperate bug in the convenience layer: #50