Add mdadm guide

docs/armbian.md

@@ -28,4 +28,4 @@ You will be prompted with a selection menu for a build option, a board name, a k
 
 Build process uses caching for the compilation and the debootstrap process, so consecutive runs with similar settings will be much faster.
 
-*Source: https://github.com/armbian/build/blob/master/README.md*
+*Source: [link](https://github.com/armbian/build/blob/master/README.md)*

docs/mdadm.md

@@ -0,0 +1,236 @@
+The **mdadm** utility can be used to create and manage storage arrays using Linux's software RAID capabilities.
+
+In this guide, we will show how to create different RAID configurations :
+
+* RAID1 (for 2x HDD)
+* RAID6 (for 4x HDD)
+* RAID10 (for 4x HDD)
+
+## Install mdadm
+
+    sudo apt-get install mdadm
+
+## Identify you Storage Drives
+
+To get started, you will need find to identify storage drives that you will be using to compose your RAID array:
+
+    lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINT
+
+Output
+
+    NAME          SIZE FSTYPE TYPE MOUNTPOINT
+    sda           1.8T        disk
+    sdb           1.8T        disk
+    sdc           1.8T        disk
+    sdd           1.8T        disk
+    mmcblk0      14.9G        disk
+    └─mmcblk0p1  14.7G ext4   part /
+    zram0          50M        disk /var/log
+    zram1       504.4M        disk [SWAP]
+    zram2       504.4M        disk [SWAP]
+
+As you can see above, we have four drives without a filesystem, each of 1.8TB in size. So our drives are /dev/sda, /dev/sdb, /dev/sdc and /dev/sdd.
+
+!!! note
+    To avoid any confusion at identifying the right drive, start Helios4 without any type of USB storage connected to it.
+
+## Create RAID 1 Array
+
+### Step 1 - Create the array
+
+To create a RAID 1 array with 2x drives, pass them in to the mdadm --create command. You will have to specify the device name you wish to create (**/dev/md0** in our case), the RAID level, and the number of devices:
+
+    sudo mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda /dev/sdb
+
+If the drives you are using are not partitioned with the boot flag enabled, you will likely be given the following warning. It is safe to type y to continue:
+
+    mdadm: Note: this array has metadata at the start and
+        may not be suitable as a boot device.  If you plan to
+        store '/boot' on this device please ensure that
+        your boot-loader understands md/v1.x metadata, or use
+        --metadata=0.90
+    mdadm: size set to 1953383488K
+    mdadm: automatically enabling write-intent bitmap on large array
+    Continue creating array? y
+    mdadm: Defaulting to version 1.2 metadata
+    mdadm: array /dev/md0 started.
+
+
+The mdadm tool will start to mirror the drives. This can take some time to complete, but the array can be used during this time. You can monitor the progress of the mirroring by checking the /proc/mdstat file:
+
+    cat /proc/mdstat
+
+Output
+
+    Personalities : [raid1]
+    md0 : active raid1 sdb[1] sda[0]
+        1953383488 blocks super 1.2 [2/2] [UU]
+        [>....................]  resync =  0.9% (19054272/1953383488) finish=213.6min speed=150885K/sec
+        bitmap: 15/15 pages [60KB], 65536KB chunk
+
+    unused devices: <none>
+
+As you can see in the first line, the /dev/md0 device has been created with the RAID 1 configuration using the /dev/sda and /dev/sdb devices. The fourth line shows the progress on the mirroring. You can continue the guide while this process completes.
+
+### Step 2 - Create and Mount the Filesystem
+
+Create a filesystem on the array:
+
+    sudo mkfs.ext4 -F /dev/md0
+
+Create a mount point to attach the new filesystem:
+
+    sudo mkdir -p /mnt/md0
+
+You can mount the filesystem by typing:
+
+    sudo mount /dev/md0 /mnt/md0
+
+Check whether the new space is available by typing:
+
+    df -h -x devtmpfs -x tmpfs
+
+Output
+
+    Filesystem      Size  Used Avail Use% Mounted on
+    /dev/mmcblk0p1   15G  842M   14G   6% /
+    /dev/zram0       49M  784K   45M   2% /var/log
+    /dev/md0        1.8T   77M  1.7T   1% /mnt/md0
+
+
+The new filesystem is mounted and accessible.
+
+### Step 3 - Save the Array Layout
+
+To make sure that the array is reassembled automatically at boot, we will have to adjust the /etc/mdadm/mdadm.conf file. You can automatically scan the active array and append the file by typing:
+
+    sudo mdadm --detail --scan | sudo tee -a /etc/mdadm/mdadm.conf
+
+Afterwards, you can update the initramfs, so that the array will be available during the early boot stage:
+
+    sudo update-initramfs -u
+
+Add the new filesystem mount options to the /etc/fstab file for automatic mounting at boot:
+
+    echo '/dev/md0 /mnt/md0 ext4 defaults,nofail,discard 0 0' | sudo tee -a /etc/fstab
+
+**Your RAID 1 array should now automatically be assembled and mounted each boot!**
+
+## Create RAID 6 Array
+
+    sudo mdadm --create --verbose /dev/md0 --level=6 --raid-devices=4 /dev/sda /dev/sdb /dev/sdc /dev/sdd
+
+The mdadm tool will start to mirror the drives. This can take some time to complete, but the array can be used during this time. You can monitor the progress of the mirroring by checking the /proc/mdstat file:
+
+    cat /proc/mdstat
+
+Output
+
+    Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10]
+    md0 : active raid6 sdd[3] sdc[2] sdb[1] sda[0]
+          209584128 blocks super 1.2 level 6, 512k chunk, algorithm 2 [4/4] [UUUU]
+          [>....................]  resync =  0.6% (668572/104792064) finish=10.3min speed=167143K/sec
+
+    unused devices: <none>
+
+As you can see in the first line, the /dev/md0 device has been created with the RAID 1 configuration using the /dev/sda and /dev/sdb devices. The fourth line shows the progress on the mirroring. You can continue the guide while this process completes.
+
+
+
+Then refer to [Step2](#step-2-create-and-mount-the-filesystem) and [Step3](#step-3-save-the-array-layout) of the RAID1 section.
+
+## Create RAID 10 Array
+
+    sudo mdadm --create --verbose /dev/md0 --level=10 --raid-devices=4 /dev/sda /dev/sdb /dev/sdc /dev/sdd
+
+The mdadm tool will start to mirror the drives. This can take some time to complete, but the array can be used during this time. You can monitor the progress of the mirroring by checking the /proc/mdstat file:
+
+    cat /proc/mdstat
+
+Output
+
+    Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10]
+    md0 : active raid10 sdd[3] sdc[2] sdb[1] sda[0]
+          209584128 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
+          [===>.................]  resync = 18.1% (37959424/209584128) finish=13.8min speed=206120K/sec
+
+    unused devices: <none>
+
+As you can see in the first line, the /dev/md0 device has been created with the RAID 1 configuration using the /dev/sda and /dev/sdb devices. The fourth line shows the progress on the mirroring. You can continue the guide while this process completes.
+
+Then refer to [Step2](#step-2-create-and-mount-the-filesystem) and [Step3](#step-3-save-the-array-layout) of the RAID1 section.
+
+## Reset Existing RAID Devices
+
+!!! warning
+    This process will completely destroy the array and any data written to it. Make sure that you are operating on the correct array and that you have copied off any data you need to retain prior to destroying the array.
+
+Find the active arrays in the /proc/mdstat file by typing:
+
+    cat /proc/mdstat
+
+Output
+
+    Personalities : [raid0] [linear] [multipath] [raid1] [raid6] [raid5] [raid4] [raid10]
+    md0 : active raid0 sdc[1] sdd[0]
+          209584128 blocks super 1.2 512k chunks
+
+    unused devices: <none>
+
+Unmount the array from the filesystem:
+
+    sudo umount /dev/md0
+
+Then, stop and remove the array by typing:
+
+    sudo mdadm --stop /dev/md0
+    sudo mdadm --remove /dev/md0
+
+Find the devices that were used to build the array with the following command:
+
+    lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINT
+
+Output
+
+    NAME          SIZE FSTYPE            TYPE  MOUNTPOINT
+    sda           1.8T linux_raid_member disk  
+    └─md0         1.8T ext4              raid1 /mnt/md0
+    sdb           1.8T linux_raid_member disk  
+    └─md0         1.8T ext4              raid1 /mnt/md0
+    mmcblk0      14.9G                   disk  
+    └─mmcblk0p1  14.7G ext4              part  /
+    zram0          50M                   disk  /var/log
+    zram1       504.4M                   disk  [SWAP]
+    zram2       504.4M                   disk  [SWAP]
+
+!!! important
+    Keep in mind that the /dev/sd* names can change any time you reboot! Check them every time to make sure you are operating on the correct devices.
+
+After discovering the devices used to create an array, zero their superblock to reset them to normal:
+
+    sudo mdadm --zero-superblock /dev/sda
+    sudo mdadm --zero-superblock /dev/sdb
+
+You should remove any of the persistent references to the array. Edit the /etc/fstab file and comment out or remove the reference to your array:
+
+```bash
+sudo nano /etc/fstab
+
+# /dev/md0 /mnt/md0 ext4 defaults,nofail,discard 0 0
+```
+
+Also, comment out or remove the array definition from the /etc/mdadm/mdadm.conf file:
+
+```bash
+sudo nano /etc/mdadm/mdadm.conf
+
+# ARRAY /dev/md0 metadata=1.2 name=mdadmwrite:0 UUID=7261fb9c:976d0d97:30bc63ce:85e76e91
+```
+
+Finally, update the initramfs again:
+
+    sudo update-initramfs -u
+
+At this point, you should be ready to reuse the storage devices individually, or as components of a different array.
+
+*Tuto Source: [link](https://www.digitalocean.com/community/tutorials/how-to-create-raid-arrays-with-mdadm-on-ubuntu-16-04)*

mkdocs.yml

@@ -62,6 +62,7 @@ pages:
 - Software:
   - U-Boot : 'uboot.md'
   - Armbian : 'armbian.md'
+  - Mdadm (RAID) : 'mdadm.md'
   - OpenMediaVault : 'omv.md'
   - Syncloud : 'syncloud.md'
   - FreeBSD : 'freebsd.md'