btrfs-progs: Add device management related paragraph.

Add device management related paragraph to better explain btrfs device
management.

Cc: Marc MERLIN <marc@merlins.org>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>

Documentation/btrfs-balance.txt

@@ -14,6 +14,8 @@ DESCRIPTION
 'btrfs balance' is used to balance chunks in a btrfs filesystem across
 multiple or even single device.
 
+See `btrfs-device`(8) for more details about the effect on device management.
+
 SUBCOMMAND
 ----------
 <path>::
@@ -75,3 +77,4 @@ further details.
 SEE ALSO
 --------
 `mkfs.btrfs`(8),
+`btrfs-device`(8)

Documentation/btrfs-device.txt

@@ -14,6 +14,46 @@ DESCRIPTION
 'btrfs device' is used to control the btrfs devices, since btrfs can be used
 across several devices, 'btrfs device' is used for multiple device management.
 
+DEVICE MANAGEMENT
+-----------------
+Btrfs filesystem is capable to manage multiple devices.
+
+Btrfs filesystem uses different profiles to manage different RAID level, and
+use balance to rebuild chunks, also devices can be added/removed/replace
+online.
+
+Profile::
+Btrfs filesystem uses data/metadata profiles to manage allocation/duplication
+mechanism. Profiles like RAID level can be assigned to data and metadata separately.
++
+See `mkfs.btrfs`(8) for more details.
+
+RAID level::
+Btrfs filesystem supports most of the standard RAID level: 0/1/5/6/10.
+RAID levels can be assigned at mkfs time or online.
++
+See `mkfs.btrfs`(8) for mkfs time RAID level assign and `btrfs-balance`(8) for
+online RAID level assign.
+
+Balance::
+`btrfs-balance`(8) subcommand can be used to balance or rebuild chunks to the
+desired profile.
++
+Due to the fact that balance can rebuild/recovery chunks according to its RAID
+duplication if possible, so when using RAID1/5/6/10 with some devices failed
+and you just added a new device to btrfs using `btrfs-device`(8), you should
+run `btrfs-balance`(8) to rebuild the chunks.
++
+See `btrfs-balance`(8) for more details.
+
+Device add/remove/replace::
+Device can be added/removed using `btrfs-replace`(8) subcommand and replaced
+using `btrfs-replace`(8).
++
+When device is removed or replaced, btrfs will do the chunk rebuild if needed.
++
+See `btrfs-replace`(8) and this man page for more details.
+
 SUBCOMMAND
 ----------
 'add' [-Kf] <dev> [<dev>...] <path>::
@@ -73,3 +113,5 @@ further details.
 SEE ALSO
 --------
 `mkfs.btrfs`(8),
+`btrfs-replace`(8),
+`btrfs-balance`(8)

Documentation/btrfs-replace.txt

@@ -13,6 +13,12 @@ DESCRIPTION
 -----------
 'btrfs replace' is used to replace btrfs managed devices with other device.
 
+Note: this is not currently supported for RAID5/6 profiles and must use the
+device add/delete workaround.
+
+It is recommended to see `btrfs-device`(8) for more details about btrfs device
+management.
+
 SUBCOMMAND
 ----------
 'start' [-Bfr] <srcdev>|<devid> <targetdev> <path>::
@@ -74,3 +80,4 @@ further details.
 SEE ALSO
 --------
 `mkfs.btrfs`(8),
+`btrfs-device`(8),