16 KiB
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
Fix mdadm
You might see the following error message in your boot messages "mdadm: initramfs boot message: /scripts/local-bottom/mdadm: rm: not found"
To fix this minor issue simply edit the mdadm hook script of initramfs:
sudo nano /usr/share/initramfs-tools/hooks/mdadm
Add copy_exec /bin/rm /bin after the following lines:
copy_exec /sbin/mdadm /sbin
copy_exec /sbin/mdmon /sbin
Then update initramfs:
sudo update-initramfs -u
Identify you Storage Drives
To get started, you will need first to identify the storage drives that you will use 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 Array
Create RAID 1 Array
To create a RAID 1 array with 2x drives, pass them 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 second 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.
Create RAID 6 Array
To create a RAID 6 array with 4x drives, pass them 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=6 --raid-devices=4 /dev/sda /dev/sdb /dev/sdc /dev/sdd
The mdadm tool will start to configure the array (it actually uses the recovery process to build the array for performance reasons). 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] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid6 sdd[3] sdc[2] sdb[1] sda[0]
3906766848 blocks super 1.2 level 6, 512k chunk, algorithm 2 [4/4] [UUUU]
[>....................] resync = 0.3% (7171152/1953383424) finish=471.0min speed=68866K/sec
bitmap: 15/15 pages [60KB], 65536KB chunk
unused devices: <none>
As you can see in the second line, the /dev/md0 device has been created with the RAID 6 configuration using the /dev/sda, /dev/sdb, /dev/sdc and /dev/sdd devices. The fourth line shows the progress on the mirroring. You can continue the guide while this process completes.
Create RAID 10 Array
To create a RAID 10 array with 4x drives, pass them 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=10 --raid-devices=4 /dev/sda /dev/sdb /dev/sdc /dev/sdd
The mdadm tool will start to configure the array (it actually uses the recovery process to build the array for performance reasons). 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] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid10 sdd[3] sdc[2] sdb[1] sda[0]
3906766848 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
[>....................] resync = 0.5% (20708608/3906766848) finish=305.0min speed=212294K/sec
bitmap: 30/30 pages [120KB], 65536KB chunk
unused devices: <none>
As you can see in the second line, the /dev/md0 device has been created with the RAID 10 configuration using the /dev/sda, /dev/sdb, /dev/sdc and /dev/sdd devices. The fourth line shows the progress on the mirroring. You can continue the guide while this process completes.
Create and Mount the Filesystem
!!! note The Helios4 System-On-Chip is a 32bit architecture, therefore the max partition size supported is 16TB. If your RAID array is more than 16TB of usable space, then you will need to create more than just one partition. You can use fdisk /dev/md0 command to create several partitions on your array, then instead of using /dev/md0 for the below commands, it will be /dev/md0p1, /dev/md0p2, etc...
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.
Save the Array Layout
To make sure that the array is reassembled automatically at boot, we will have to modify /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 array should now automatically be assembled and mounted at each boot!
Check your RAID Array State
To get a detailed picture of your array setup and its state you can use the following command:
sudo mdadm -D /dev/md0
This is the output when the array is in good health, you can see the line showing State : clean.
/dev/md0:
Version : 1.2
Creation Time : Sun Jul 29 14:59:58 2018
Raid Level : raid10
Array Size : 3906766848 (3725.78 GiB 4000.53 GB)
Used Dev Size : 1953383424 (1862.89 GiB 2000.26 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Tue Nov 13 06:21:03 2018
State : clean
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Layout : near=2
Chunk Size : 512K
Name : helios4:0 (local to host helios4)
UUID : ea143418:153e050e:ac86d56c:07547815
Events : 95892
Number Major Minor RaidDevice State
0 8 0 0 active sync set-A /dev/sda
1 8 16 1 active sync set-B /dev/sdb
2 8 32 2 active sync set-A /dev/sdc
3 8 48 3 active sync set-B /dev/sdd
In below example the array has a failed drive, you can see the line State : clean, degraded and that the RaidDevice 2 (/dev/sdc) is removed. The array is still active but in a degraded state because it requires /dev/sdc to be replaced as soon as possible.
/dev/md0:
Version : 1.2
Creation Time : Sun Jul 29 14:59:58 2018
Raid Level : raid10
Array Size : 3906766848 (3725.78 GiB 4000.53 GB)
Used Dev Size : 1953383424 (1862.89 GiB 2000.26 GB)
Raid Devices : 4
Total Devices : 3
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Tue Nov 13 08:34:06 2018
State : clean, degraded
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Layout : near=2
Chunk Size : 512K
Name : helios4:0 (local to host helios4)
UUID : ea143418:153e050e:ac86d56c:07547815
Events : 95892
Number Major Minor RaidDevice State
0 8 0 0 active sync set-A /dev/sda
1 8 16 1 active sync set-B /dev/sdb
- 0 0 2 removed /dev/sdc
3 8 48 3 active sync set-B /dev/sdd
2 8 32 - faulty /dev/sdc
Replace a Failed Drive
Once you have identified the failed drive with the command mdadm -D, as shown in the previous section, you will need to do the following steps to replace the failed drive:
-
Mark the faulty drive as failed.
mdadm /dev/md0 --fail /dev/sdc -
Remove the drive from the array.
mdadm /dev/md0 --remove /dev/sdc -
Identify which physical drive is to be replaced.
readlink -f on /sys/block/* | grep sdc/sys/devices/platform/soc/soc:internal-regs/f10e0000.sata/ata3/host2/target2:0:0/2:0:0:0/block/sdcIn this example the faulty drive is the one connected to the SATA port 3 (ata3) of the board.
-
Shutdown your system and replace the faulty drive.
sudo halt -
Power-up your Helios4.
-
Add the new drive to the array. You will need to use lsblk command to figure out what the device name of the new drive. Most probably it will be the same than before.
sudo mdadm /dev/md0 --add /dev/sdc
Finally check the array is correctly re-building the new drive.
sudo mdadm -d /dev/md0
Number Major Minor RaidDevice State
0 8 0 0 active sync set-A /dev/sda
1 8 16 1 active sync set-B /dev/sdb
4 0 0 2 spare rebuilding /dev/sdc
3 8 48 3 active sync set-B /dev/sdd
We can see that /dev/sdc is being rebuilt.
cat /proc/mdstat
Personalities : [raid1] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid10 sdd[3] sdc[4] sdb[1] sda[0]
3906766848 blocks super 1.2 512K chunks 2 near-copies [4/4] [UU_U]
[>....................] recovery = 0.5% (20708608/3906766848) finish=305.0min speed=212294K/sec
You can see the rebuild progress.
Setup Error Notification (Recommended)
In order to get notified or to see visual indication that something is wrong with your array you can configure email alerts and/or error LED.
Configure Email Alerts
Receive a notification whenever mdadm detects something wrong with your array. This is very important since you don't want to miss out an issue on your array and have time to take the right actions.
sudo nano /etc/mdadm/mdadm.conf
Edit the following section and replace root by your email address.
# instruct the monitoring daemon where to send mail alerts
MAILADDR root
!!! important You will need to install and configure postfix or sendmail.
Configure Error LED
!!! note To be done.
Test alerts
You can test your error notification setup by doing the following:
sudo systemctl stop mdmonitor.service
sudo mdadm --monitor --scan --test -1
sudo systemctl start mdmonitor.service
Import an Existing RAID Array
If for some reasons you want to add an existing array to your system (e.g you just did a new install of your operating system), you can use the following command to detect your existing array.
sudo mdadm —assemble —scan
Then refer to previous sections to mount the file system of this existing array and save its layout in mdadm configuration.
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 raid6 sdd[3] sdc[2] sdb[1] sda[0]
3906766848 blocks super 1.2 level 6, 512k chunk
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 3.7T ext4 raid6
sdb 1.8T linux_raid_member disk
└─md0 3.7T ext4 raid6
sdc 1.8T linux_raid_member disk
└─md0 3.7T ext4 raid6
sdd 1.8T linux_raid_member disk
└─md0 3.7T ext4 raid6
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
sudo mdadm --zero-superblock /dev/sdc
sudo mdadm --zero-superblock /dev/sdd
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:
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:
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 devices of a different array.
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