dedupe: if percentage is 100, don't go through random + math

[fio.git] / fio.1

diff --git a/fio.1 b/fio.1
index b5ff3ccbc4633dd0cf92ad42a59efe660d64e848..bc6c9fa655e8eefe13d410013309679dcf2eb7e5 100644 (file)
--- a/fio.1
+++ b/fio.1
@@ -478,7 +478,15 @@ size, fio can alternate random and zeroed data throughout the IO buffer.
 If set, fio will fill the IO buffers with this pattern. If not set, the contents
 of IO buffers is defined by the other options related to buffer contents. The
 setting can be any pattern of bytes, and can be prefixed with 0x for hex
-values.
+values. It may also be a string, where the string must then be wrapped with
+"".
+.TP
+.BI dedupe_percentage \fR=\fPint
+If set, fio will generate this percentage of identical buffers when writing.
+These buffers will be naturally dedupable. The contents of the buffers depend
+on what other buffer compression settings have been set. It's possible to have
+the individual buffers either fully compressible, or not at all. This option
+only controls the distribution of unique buffers.
 .TP
 .BI nrfiles \fR=\fPint
 Number of files to use for this job.  Default: 1.
@@ -613,8 +621,16 @@ Using Glusterfs libgfapi async interface to direct access to Glusterfs volumes w
 having to go through FUSE. This ioengine defines engine specific
 options.
 .TP
-.B hdfs
-Read and write through Hadoop (HDFS)
+.B libhdfs
+Read and write through Hadoop (HDFS).  The \fBfilename\fR 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.
 .RE
 .P
 .RE