HTGWA: Create a RAID array in Linux with mdadm

It is a easy information, a part of a collection I will name 'How-To Information With out Advertisements'. In it, I'll doc how I create and mount a RAID array in Linux with mdadm.

Within the information, I will create a RAID 0 array, however different sorts might be created by specifying the correct --level within the mdadm create command.

Put together the disks

You need to have at the very least two drives arrange and able to go. And be sure you do not care about something on them. They're gonna get erased. And be sure you do not care in regards to the integrity of the information you are going to retailer on the RAID 0 quantity. RAID 0 is sweet for pace... and that is about it. Any drive fails, all of your knowledge's gone.

Word: Different guides, like this excellent one on the Unix StackExchange site, have much more element. That is only a fast and soiled information.

Listing all of the units in your system:

$ lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda           8:0    0  7.3T  0 disk 
└─sda1        8:1    0  7.3T  0 half /mnt/mydrive
sdb           8:16   0  7.3T  0 disk 
sdc           8:32   0  7.3T  0 disk 
sdd           8:48   0  7.3T  0 disk 
sde           8:64   0  7.3T  0 disk 
nvme0n1     259:0    0  7.3T  0 disk 
└─nvme0n1p1 259:1    0  7.3T  0 half /

I need to RAID collectively sda via sde (loopy, I do know). I observed that sda already has a partition and a mount. We should always make sure that all of the drives that will likely be a part of the array are partition-free:

$ sudo umount /dev/sda?; sudo wipefs --all --force /dev/sda?; sudo wipefs --all --force /dev/sda
$ sudo umount /dev/sdb?; sudo wipefs --all --force /dev/sdb?; sudo wipefs --all --force /dev/sdb
...

Do this for every of the drives. If you happen to did not notice it but, this wipes all the things. It would not zero the information, so technically it may nonetheless be recovered at this level!

Examine to ensure nothing's mounted (and be sure you have eliminated any of the drives you may use within the array from /and so on/fstab in case you had persistent mounts for them in there!):

$ lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda           8:0    0  7.3T  0 disk 
sdb           8:16   0  7.3T  0 disk 
sdc           8:32   0  7.3T  0 disk 
sdd           8:48   0  7.3T  0 disk 
sde           8:64   0  7.3T  0 disk 
nvme0n1     259:0    0  7.3T  0 disk 
└─nvme0n1p1 259:1    0  7.3T  0 half /

Trying good, time to start out constructing the array!

Partition the disks with sgdisk

You may interactively do that with gdisk, however I like extra automation, so I take advantage of sgdisk. If it isn't put in, and also you're on a Debian-like distro, set up it: sudo apt set up -y gdisk.

sudo sgdisk -n 1:0:0 /dev/sda
sudo sgdisk -n 1:0:0 /dev/sdb
...

Do this for every of the drives.

WARNING: Coming into the incorrect instructions right here will wipe knowledge in your valuable drives. You've got been warned. Once more.

Confirm there's now a partition for every drive:

pi@taco:~ $ lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda           8:0    0  7.3T  0 disk 
└─sda1        8:1    0  7.3T  0 half 
sdb           8:16   0  7.3T  0 disk 
└─sdb1        8:17   0  7.3T  0 half 
sdc           8:32   0  7.3T  0 disk 
└─sdc1        8:33   0  7.3T  0 half 
sdd           8:48   0  7.3T  0 disk 
└─sdd1        8:49   0  7.3T  0 half 
sde           8:64   0  7.3T  0 disk 
└─sde1        8:65   0  7.3T  0 half 
...

Create a RAID 0 array with mdadm

If you do not have mdadm put in, and also you're on a Debian-like system, run sudo apt set up -y mdadm.

$ sudo mdadm --create --verbose /dev/md0 --level=0 --raid-devices=5 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1
mdadm: chunk dimension defaults to 512K
mdadm: Defaulting to model 1.2 metadata
mdadm: array /dev/md0 began.

You may specify totally different RAID ranges with the --level choice above. Sure ranges require sure numbers of drives to work appropriately!

Confirm the array is working

For RAID 0, it ought to instantly present State : clear when operating the command beneath. For different RAID ranges, it could take some time to initially resync or do different operations.

$ sudo mdadm --detail /dev/md0
/dev/md0:
           Model : 1.2
     Creation Time : Wed Nov 10 18:05:57 2021
        Raid Degree : raid0
        Array Measurement : 39069465600 (37259.55 GiB 40007.13 GB)
      Raid Units : 5
     Complete Units : 5
       Persistence : Superblock is persistent

       Replace Time : Wed Nov 10 18:05:57 2021
             State : clear 
    Lively Units : 5
   Working Units : 5
    Failed Units : 0
     Spare Units : 0

        Chunk Measurement : 512K

Consistency Coverage : none

              Title : taco:0  (native to host taco)
              UUID : a5043664:c01dac00:73e5a8fc:2caf5144
            Occasions : 0

    Quantity   Main   Minor   RaidDevice State
       0       8        1        0      lively sync   /dev/sda1
       1       8       17        1      lively sync   /dev/sdb1
       2       8       33        2      lively sync   /dev/sdc1
       3       8       49        3      lively sync   /dev/sdd1
       4       8       65        4      lively sync   /dev/sde1

You observe the progress of a rebuild (if selecting a stage moreover RAID 0, this may take a while) with watch cat /proc/mdstat. Ctrl-C to exit.

Persist the array configuration to mdadm.conf

$ sudo mdadm --detail --scan --verbose | sudo tee -a /and so on/mdadm/mdadm.conf

If you happen to do not do that, the RAID array will not come up after a reboot. That might be unhappy.

Format the array

$ sudo mkfs.ext4 -m 0 -E lazy_itable_init=0,lazy_journal_init=0 /dev/md0
mke2fs 1.44.5 (15-Dec-2018)
Discarding system blocks: achieved                            
Creating filesystem with 9767366400 4k blocks and 610461696 inodes
Filesystem UUID: 5d3b012c-e5f6-49d1-9014-1c61e982594f
Superblock backups saved on blocks: 
    32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
    4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 
    102400000, 214990848, 512000000, 550731776, 644972544, 1934917632, 
    2560000000, 3855122432, 5804752896

Allocating group tables: achieved                            
Writing inode tables: achieved                            
Creating journal (262144 blocks): achieved
Writing superblocks and filesystem accounting data: achieved 

On this instance, I used lazy initialization to keep away from the (very) lengthy means of initializing all of the inodes. For big arrays, particularly with model new drives that aren't filled with outdated information, there is no sensible motive to do it the 'regular'/non-lazy approach (at the very least, AFAICT).

Mount the array

Checking on our array with lsblk now, we will see all of the members of md0:

$ lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
sda           8:0    0  7.3T  0 disk  
└─sda1        8:1    0  7.3T  0 half  
  └─md0       9:0    0 36.4T  0 raid0 
sdb           8:16   0  7.3T  0 disk  
└─sdb1        8:17   0  7.3T  0 half  
  └─md0       9:0    0 36.4T  0 raid0 
sdc           8:32   0  7.3T  0 disk  
└─sdc1        8:33   0  7.3T  0 half  
  └─md0       9:0    0 36.4T  0 raid0 
sdd           8:48   0  7.3T  0 disk  
└─sdd1        8:49   0  7.3T  0 half  
  └─md0       9:0    0 36.4T  0 raid0 
sde           8:64   0  7.3T  0 disk  
└─sde1        8:65   0  7.3T  0 half  
  └─md0       9:0    0 36.4T  0 raid0 

Now make a mount level and mount the amount:

$ sudo mkdir /mnt/raid0
$ sudo mount /dev/md0 /mnt/raid0

Confirm the mount exhibits up with df

$ df -h
Filesystem      Measurement  Used Avail Use% Mounted on
...
/dev/md0         37T   24K   37T   1% /mnt/raid0

Make the mount persist

If you happen to do not add the mount to /and so on/fstab, it will not be mounted after you reboot!

First, get the UUID of the array (the worth contained in the quotations within the output beneath):

$ sudo blkid
...
/dev/md0: UUID="5d3b012c-e5f6-49d1-9014-1c61e982594f" TYPE="ext4"

Then, edit /and so on/fstab (e.g. sudo nano /and so on/fstab) and add a line like the next to the tip:

UUID=5d3b012c-e5f6-49d1-9014-1c61e982594f /mnt/raid0 ext4 defaults 0 0

Save that file and reboot.

Word: If genfstab is obtainable in your system, use it as an alternative. A lot much less more likely to asplode issues: genfstab -U /mnt/mydrive >> /mnt/and so on/fstab.

Confirm the mount endured.

After reboot:

$ df -h
Filesystem      Measurement  Used Avail Use% Mounted on
...
/dev/md0         37T   24K   37T   1% /mnt/raid0

Drop the array

If you would like to drop or take away the RAID array and reset all of the disk partitions so you might use them in one other array, or individually, it's essential to do the next:

  1. Edit /and so on/fstab and delete the road for the /mnt/raid0 mount level.
  2. Edit /and so on/mdadm/mdadm.conf and delete the strains you added earlier through mdadm | tee.
  3. Unmount the amount: sudo umount /mnt/raid0
  4. Wipe the ext4 filesystem: sudo wipefs --all --force /dev/md0
  5. Cease the RAID quantity: sudo mdadm --stop /dev/md0
  6. Zero the superblock on all of the drives: sudo mdadm --zero-superblock /dev/sda1 /dev/sdb1 ...

At this level, you must have again all of the drives that have been a part of the array and might do different issues with them.



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