Update libhdfs engine documention and options
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/HOWTO b/HOWTO
index d728353..a0b89c8 100644
--- a/HOWTO
+++ b/HOWTO
@@ -694,7 +694,21 @@
having to go through FUSE. This ioengine
defines engine specific options.
- hdfs Read and write through Hadoop (HDFS).
+ libhdfs Read and write through Hadoop (HDFS).
+ The 'filename' option is used to specify host,
+ port of the hdfs name-node to connect. This
+ engine interprets offsets a little
+ differently. In HDFS, files once created
+ cannot be modified. So random writes are not
+ possible. To imitate this, libhdfs engine
+ expects bunch of small files to be created
+ over HDFS, and engine will randomly pick a
+ file out of those files based on the offset
+ generated by fio backend. (see the example
+ job file to create such files, use rw=write
+ option). Please note, you might want to set
+ necessary environment variables to work with
+ hdfs/libhdfs properly.
external Prefix to specify loading an external
IO engine object file. Append the engine