Update replace-brick documentation (#782)

* docs: update replace-brick notes

We no longer need to do manual steps before replacing a brick. It
is enough to use `replace-brick` without killing brick processes
or setting xattrs manually (this has been true for *years*).

* docs: minor improvements to replace-brick text

Use code blocks for brick name and simplify formatting in places
to be consistent with other examples. Also, it seems that MkDocs
renders this Markdown slightly differently than GitHub.

* docs: reverse order of pure vs distributed replicate

The "pure" replicate example comes first in the docs, so it seems
natural to list it first here.

* Update docs/Administrator-Guide/Managing-Volumes.md

Co-authored-by: Karthik Subrahmanya <[email protected]>

---------

Co-authored-by: Karthik Subrahmanya <[email protected]>

docs/Administrator-Guide/Managing-Volumes.md

@@ -185,7 +185,7 @@ operation to migrate data from the removed-bricks to the rest of the volume.
 
 To replace a brick on a distribute only volume, add the new brick and then remove the brick you want to replace. This will trigger a rebalance operation which will move data from the removed brick.
 
-> NOTE: Replacing a brick using the 'replace-brick' command in gluster is supported only for distributed-replicate or _pure_ replicate volumes.
+> NOTE: Replacing a brick using the 'replace-brick' command in gluster is supported only for _pure_ replicate or distributed-replicate volumes.
 
 Steps to remove brick Server1:/home/gfs/r2_1 and add Server1:/home/gfs/r2_2:
 
@@ -265,73 +265,9 @@ This section of the document describes how brick: `Server1:/home/gfs/r2_0` is re
 
 Steps:
 
-1.  Make sure there is no data in the new brick Server1:/home/gfs/r2_5
+1.  Make sure there is no data in the new brick `Server1:/home/gfs/r2_5`
 2.  Check that all the bricks are running. It is okay if the brick that is going to be replaced is down.
-3.  Bring the brick that is going to be replaced down if not already.
-
-    - Get the pid of the brick by executing 'gluster volume <volname> status'
-
-           # gluster volume status
-           Status of volume: r2
-           Gluster process                        Port    Online    Pid
-           ------------------------------------------------------------------------------
-           Brick Server1:/home/gfs/r2_0            49152    Y    5342
-           Brick Server2:/home/gfs/r2_1            49153    Y    5354
-           Brick Server1:/home/gfs/r2_2            49154    Y    5365
-           Brick Server2:/home/gfs/r2_3            49155    Y    5376
-
-    - Login to the machine where the brick is running and kill the brick.
-
-           # kill -15 5342
-
-    - Confirm that the brick is not running anymore and the other bricks are running fine.
-
-           # gluster volume status
-           Status of volume: r2
-           Gluster process                        Port    Online    Pid
-           ------------------------------------------------------------------------------
-           Brick Server1:/home/gfs/r2_0            N/A      N    5342 <<---- brick is not running, others are running fine.
-           Brick Server2:/home/gfs/r2_1            49153    Y    5354
-           Brick Server1:/home/gfs/r2_2            49154    Y    5365
-           Brick Server2:/home/gfs/r2_3            49155    Y    5376
-
-4.  Using the gluster volume fuse mount (In this example: `/mnt/r2`) set up metadata so that data will be synced to new brick (In this case it is from `Server1:/home/gfs/r2_1` to `Server1:/home/gfs/r2_5`)
-
-    - Create a directory on the mount point that doesn't already exist. Then delete that directory, do the same for metadata changelog by doing setfattr. This operation marks the pending changelog which will tell self-heal damon/mounts to perform self-heal from `/home/gfs/r2_1` to `/home/gfs/r2_5`.
-
-           mkdir /mnt/r2/<name-of-nonexistent-dir>
-           rmdir /mnt/r2/<name-of-nonexistent-dir>
-           setfattr -n trusted.non-existent-key -v abc /mnt/r2
-           setfattr -x trusted.non-existent-key  /mnt/r2
-
-    - Check that there are pending xattrs on the replica of the brick that is being replaced:
-
-           getfattr -d -m. -e hex /home/gfs/r2_1
-           # file: home/gfs/r2_1
-           security.selinux=0x756e636f6e66696e65645f753a6f626a6563745f723a66696c655f743a733000
-           trusted.afr.r2-client-0=0x000000000000000300000002 <<---- xattrs are marked from source brick Server2:/home/gfs/r2_1
-           trusted.afr.r2-client-1=0x000000000000000000000000
-           trusted.gfid=0x00000000000000000000000000000001
-           trusted.glusterfs.dht=0x0000000100000000000000007ffffffe
-           trusted.glusterfs.volume-id=0xde822e25ebd049ea83bfaa3c4be2b440
-
-5.  Volume heal info will show that '/' needs healing.(There could be more entries based on the work load. But '/' must exist)
-
-            # gluster volume heal r2 info
-            Brick Server1:/home/gfs/r2_0
-            Status: Transport endpoint is not connected
-
-            Brick Server2:/home/gfs/r2_1
-            /
-            Number of entries: 1
-
-            Brick Server1:/home/gfs/r2_2
-            Number of entries: 0
-
-            Brick Server2:/home/gfs/r2_3
-            Number of entries: 0
-
-6.  Replace the brick with 'commit force' option. Please note that other variants of replace-brick command are not supported.
+3.  Replace the brick with 'commit force' option. Please note that other variants of replace-brick command are not supported.
 
     - Execute replace-brick command
 
@@ -344,25 +280,14 @@ Steps:
            Status of volume: r2
            Gluster process                        Port    Online    Pid
            ------------------------------------------------------------------------------
-           Brick Server1:/home/gfs/r2_5            49156    Y    5731 <<<---- new brick is online
+           Brick Server1:/home/gfs/r2_5            49156    Y    5731 <---- new brick is online
            Brick Server2:/home/gfs/r2_1            49153    Y    5354
            Brick Server1:/home/gfs/r2_2            49154    Y    5365
            Brick Server2:/home/gfs/r2_3            49155    Y    5376
 
-    - Users can track the progress of self-heal using: `gluster volume heal [volname] info`.
-      Once self-heal completes the changelogs will be removed.
-
-            # getfattr -d -m. -e hex /home/gfs/r2_1
-            getfattr: Removing leading '/' from absolute path names
-            # file: home/gfs/r2_1
-            security.selinux=0x756e636f6e66696e65645f753a6f626a6563745f723a66696c655f743a733000
-            trusted.afr.r2-client-0=0x000000000000000000000000 <<---- Pending changelogs are cleared.
-            trusted.afr.r2-client-1=0x000000000000000000000000
-            trusted.gfid=0x00000000000000000000000000000001
-            trusted.glusterfs.dht=0x0000000100000000000000007ffffffe
-            trusted.glusterfs.volume-id=0xde822e25ebd049ea83bfaa3c4be2b440
+    - Users can track the progress of self-heal using: `gluster volume heal [volname] info`, or by checking the size of the new brick.
 
-    - `# gluster volume heal <VOLNAME> info` will show that no heal is required.
+    - `# gluster volume heal <volname> info` will show that no heal is required when the data is fully synced to the replaced brick.
 
            # gluster volume heal r2 info
            Brick Server1:/home/gfs/r2_5