doc: Adding user documentation for WORM feature

Cherry picked from commit 03813a6ec08405c815b993551d16f07075efd467:
> Change-Id: Ic31c8305254dd00eae986fbb322cac3761b5d330
> BUG: 1086760
> Signed-off-by: Kasturi Narra <knarra@redhat.com>
> Reviewed-on: http://review.gluster.org/7530
> Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
> Reviewed-by: Niels de Vos <ndevos@redhat.com>
> Reviewed-by: Lalatendu Mohanty <lmohanty@redhat.com>
> Tested-by: Gluster Build System <jenkins@build.gluster.com>

Change-Id: I5897ad47ae995ec55418dca0308dd97f00e1a1e0
BUG: 1086760
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/7732

1 files changed, 75 insertions, 0 deletions

diff --git a/doc/features/worm.md b/doc/features/worm.md
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+#WORM (Write Once Read Many)
+This features enables you to create a `WORM volume` using gluster CLI.
+##Description
+WORM (write once,read many) is a desired feature for users who want to store data such as `log files` and where data is not allowed to get modified.
+
+GlusterFS provides a new key `features.worm` which takes boolean values(enable/disable) for volume set.
+
+Internally, the volume set command with 'feature.worm' key will add 'features/worm' translator in the brick's volume file.
+
+`This change would be reflected on a subsequent restart of the volume`, i.e gluster volume stop, followed by a gluster volume start.
+
+With a volume converted to WORM, the changes are as follows:
+
+* Reads are handled normally
+* Only files with O_APPEND flag will be supported.
+* Truncation,deletion wont be supported.
+
+##Volume Options
+Use the volume set command on a volume and see if the volume is actually turned into WORM type.
+
+    # features.worm enable
+##Fully loaded Example
+WORM feature is being supported from glusterfs version 3.4
+start glusterd by using the command
+
+    # service glusterd start
+Now create a volume by using the command
+
+    # gluster volume create <vol_name> <brick_path>
+start the volume created by running the command below.
+
+    # gluster vol start <vol_name>
+Run the command below to make sure that volume is created.
+
+    # gluster volume info
+Now turn on the WORM feature on the volume by using the command
+
+    # gluster vol set <vol_name> worm enable
+Verify that the option is set by using the command
+
+    # gluster volume info
+User should be able to see another option in the volume info
+
+    # features.worm: enable
+Now restart the volume for the changes to reflect, by performing volume stop and start.
+
+    # gluster volume <vol_name> stop
+    # gluster volume <vol_name> start
+Now mount the volume using fuse mount
+
+    # mount -t glusterfs <vol_name> <mnt_point>
+create a file inside the mount point by running the command below
+
+    # touch <file_name>
+Verify that user is able to create a file by running the command below
+
+    # ls <file_name>
+
+##How To Test
+Now try deleting the above file which is been created
+
+    # rm <file_name>
+Since WORM is enabled on the volume, it gives the following error message `rm: cannot remove '/<mnt_point>/<file_name>': Read-only file system`
+
+put some content into the file which is created above.
+
+    # echo "at the end of the file" >> <file_name>
+Now try editing the file by running the commnad below and verify that the following error message is displayed `rm: cannot remove '/<mnt_point>/<file_name>': Read-only file system`
+
+    # sed -i "1iAt the beginning of the file" <file_name>
+Now read the contents of the file and verify that file can be read.
+
+    cat <file_name>
+
+`Note: If WORM option is set on the volume before it is started, then volume need not be restarted for the changes to get reflected`.