Merge pull request #681 from fett0/raid-add-documentation

Raid-1 add documentation

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+.. _raid:
+
+######
+RAID-1 
+######
+
+A Redundant Array of Independent Disks (RAID) uses two or more hard disk drives 
+to improve disk speed, store more data, and/or provide fault tolerance. 
+There are several storage schemes possible in a RAID array, each offering a 
+different combination of storage, reliability, and/or performance. 
+The VyOS system supports a “RAID 1” deployment. RAID 1 allows two or more 
+disks to mirror one another to provide system fault tolerance. In a RAID 1 
+solution, every sector of one disk is duplicated onto every sector of all 
+disks in the array. Provided even one disk in the RAID 1 set is operational, 
+the system continues to run, even through disk replacement (provided that the 
+hardware supports in-service replacement of drives). 
+RAID 1 can be implemented using special hardware or it can be implemented in 
+software. The VyOS system supports software RAID 1 on two disks.
+The VyOS implementation of RAID 1 allows the following:
+
+* Detection and reporting of disk failure
+* The ability to maintain system operation with one failed disk
+* The ability to boot the system with one failed disk
+* The ability to replace a failed disk and initiate re-mirroring
+* The ability to monitor the status of remirroring
+
+.. _raid_instalation:
+
+Installation Implications
+=========================
+
+The VyOS systems installation utility provides several options for installing 
+to a RAID 1 set. You can: 
+
+* Use the install system to create the RAID 1 set 
+* Use the underlying Linux commands to create a RAID 1 set before running the 
+  install system command.
+* Use a previously-created RAID 1 set.
+
+.. note:: Before a permanent installation, VyOS runs a live installation
+
+Configuration
+=============
+
+Single disk, install as normal 
+------------------------------
+
+When the VyOS system is installed, it automatically detects the presence of two 
+disks not currently part of a RAID array. In these cases, the VyOS 
+installation utility automatically offers you the option of configuring RAID 1 
+mirroring for the drives, with the following prompt.
+
+.. code-block:: none
+
+   Would you like to configure RAID 1 mirroring on them?
+
+* If you do not want to configure RAID 1 mirroring, enter “No” at the prompt
+  and continue with installation in the normal way.
+
+Empty 2+ Disk 
+-------------
+
+If VyOS system detect two identical disks that are not currently part of a 
+RAID-1 set, the VyOS installation utility automatically offers you the option
+of configuring RAID 1 mirroring for the drives, with the following prompt. 
+
+.. code-block:: none
+
+   Would you like to configure RAID 1 mirroring on them? 
+
+1 - To create a new RAID 1 array, enter “Yes” at the prompt. If the system 
+detects a filesystem on the partitions being used for RAID 1 it will prompt you 
+to indicate whether you want to continue creating the RAID 1 array. 
+
+.. code-block:: none
+
+   Continue creating array?
+
+2 - To overwrite the old filesystem, enter “Yes”. 
+
+3 - The system informs you that all data on both drives will be erased. You are 
+prompted to confirm that you want to continue
+
+.. code-block:: none
+
+   Are you sure you want to do this?
+
+4 - Enter “Yes” at the prompt to retain the current VyOS configuration once 
+installation is complete. Enter “No” to delete the current VyOS
+configuration. 
+
+.. code-block:: none
+
+   Would you like me to save the data on it before I delete it?
+
+5 - Enter “Yes” at the prompt to retain the current VyOS configuration once 
+installation is complete. Enter “No” to delete the current VyOS configuration.
+
+6 - Continue with installation in the normal way.
+
+
+Present RAID-1
+--------------
+
+When the VyOS software on a system with a RAID 1 set already configured, 
+the installation utility will detect the array and will display the following 
+prompt: 
+
+.. code-block:: none
+
+   Would you like to use this one? 
+
+1 - To break apart the current RAID 1 set, enter “No” at the prompt. The 
+
+installation utility detects that there are two identical disks and offers you 
+the option of configuring RAID 1 mirroring on them, displaying the following 
+prompt: 
+
+.. code-block:: none
+
+   Would you like to configure RAID 1 mirroring on them? 
+
+2 - To decline to set up a new RAID 1 configuration on the disks, enter “No” 
+at the prompt. The system prompts you to indicate which partition you would 
+like the system installed on. 
+
+.. code-block:: none
+   
+    Which partition should I install the root on? [sda1]: 
+
+3 - Enter the partition where you would like the system installed. The system 
+then prompts you to indicate whether you want to save the old configuration
+data. This represents the current VyOS configuration. 
+
+.. code-block:: none
+
+   Would you like me to save the data on it before I delete it? 
+
+4 - Enter “Yes” at the prompt to retain the current VyOS configuration once 
+installation is complete. Enter “No” to delete the current VyOS configuration. 
+
+5 - Continue with installation in the normal way.
+
+
+Detecting and Replacing a Failed RAID 1 Disk
+--------------------------------------------
+
+The VyOS system automatically detects a disk failure within a RAID 1 set and 
+reports it to the system console. You can verify the failure by issuing the
+show raid command.
+
+To replace a bad disk within a RAID 1 set, perform the following steps:
+
+1 - Remove the failed disk from the RAID 1 set by issuing the following 
+command:
+
+.. opcmd:: delete raid RAID‐1‐device member disk‐partition
+
+   where RAID-1-device is the name of the RAID 1 device (for example, md0) and 
+   disk-partition is the name of the failed disk partition (for example, sdb2).
+
+2- Physically remove the failed disk from the system. If the drives are not 
+hot-swappable, then you must shut down the system before removing the disk.
+
+3 - Replace the failed drive with a drive of the same size or larger.
+
+4 - Format the new disk for RAID 1 by issuing the following command:
+
+.. opcmd:: format <disk‐device1> like <disk‐device2>
+
+   where disk-device1 is the replacement disk (for example, sdb) and 
+   disk-device2 is the existing healthy disk (for example, sda).
+
+5-Add the replacement disk to the RAID 1 set by issuing the following command:
+
+.. opcmd:: add raid <RAID‐1‐device> member <disk‐partition>
+
+   where RAID-1-device is the name of the RAID 1 device (for example, md0) and 
+   disk-partition is the name of the replacement disk partition 
+   (for example, sdb2).
+
+Operation
+=========
+
+This part introduces how to add a disk partition to a RAID-1 set initiates
+mirror synchronization, check and display information.
+
+.. opcmd:: add raid <RAID‐1‐device> member <disk‐partition>
+ 
+   Use this command to add a member disk partition to the RAID 1 set. Adding a 
+   disk partition to a RAID 1 set initiates mirror synchronization, where all 
+   data on the existing member partition is copied to the new partition.
+
+.. opcmd:: format <disk‐device1> like <disk‐device2>
+
+   This command is typically used to prepare a disk to be added to a preexisting
+   RAID 1 set (of which disk-device2 is already a member).
+
+.. opcmd:: show raid <RAID‐1‐device>
+   
+   shows output for show raid md0 as sdb1 is being added to the RAID 1 
+   set and is in the process of being resynchronized.
+
+   .. code-block:: none
+
+      vyos@vyos:~$ show raid md0
+      /dev/md0:
+            Version : 00.90
+      Creation Time : Wed Oct 29 09:19:09 2008
+         Raid Level : raid1
+         Array Size : 1044800 (1020.48 MiB 1069.88 MB)
+      Used Dev Size : 1044800 (1020.48 MiB 1069.88 MB)
+       Raid Devices : 2
+      Total Devices : 2
+      Preferred Minor : 0
+        Persistence : Superblock is persistent
+        Update Time : Wed Oct 29 19:34:23 2008
+              State : active, degraded, recovering
+      Active Devices : 1
+      Working Devices : 2
+      Failed Devices : 0
+      Spare Devices : 1
+      Rebuild Status : 17% complete
+               UUID : 981abd77:9f8c8dd8:fdbf4de4:3436c70f
+             Events : 0.103
+        Number   Major   Minor   RaidDevice State
+           0       8        1        0      active sync   /dev/sda1
+           2       8       17        1      spare rebuilding   /dev/sdb1
+
+.. opcmd:: show raid <RAID‐1‐device>
+   
+   Use this command to display the formatting of a hard disk.
+
+   .. code-block:: none
+
+      vyos@vyos:~$ show disk sda format
+      Disk /dev/sda: 1073 MB, 1073741824 bytes
+      85 heads, 9 sectors/track, 2741 cylinders
+      Units = cylinders of 765 * 512 = 391680 bytes
+      Disk identifier: 0x000b7179   
+       Device Boot      Start         End      Blocks   Id  System
+      /dev/sda1               6        2737     1044922+  fd  Linux raid autodetect
+
+      
+