b2: implement large file uploading - fixes #456

docs/content/b2.md

@@ -1,7 +1,7 @@
 ---
 title: "B2"
 description: "Backblaze B2"
-date: "2015-12-29"
+date: "2016-06-15"
 ---
 
 <i class="fa fa-fire"></i>Backblaze B2
@@ -106,6 +106,9 @@ method to set the modification time independent of doing an upload.
 The SHA1 checksums of the files are checked on upload and download and
 will be used in the syncing process. You can use the `--checksum` flag.
 
+Large files which are uploaded in chunks will store their SHA1 on the
+object as `X-Bz-Info-large_file_sha1` as recommended by Backblaze.
+
 ### Versions ###
 
 When rclone uploads a new version of a file it creates a [new version
@@ -130,8 +133,26 @@ depending on your hardware, how big the files are, how much you want
 to load your computer, etc.  The default of `--transfers 4` is
 definitely too low for Backblaze B2 though.
 
+### Specific options ###
+
+Here are the command line options specific to this cloud storage
+system.
+
+#### --b2-chunk-size valuee=SIZE ####
+
+When uploading large files chunk the file into this size.  Note that
+these chunks are buffered in memory.  100,000,000 Bytes is the minimim
+size (default 96M).
+
+#### --b2-upload-cutoff=SIZE ####
+
+Cutoff for switching to chunked upload (default 4.657GiB ==
+5GB). Files above this size will be uploaded in chunks of
+`--b2-chunk-size`. The default value is the largest file which can be
+uploaded without chunks.
+
 ### API ###
 
 Here are [some notes I made on the backblaze
 API](https://gist.github.com/ncw/166dabf352b399f1cc1c) while
-integrating it with rclone which detail the changes I'd like to see.
+integrating it with rclone.