Software RAID 10


SSH into your server as root and run cat /proc/mdstat to view the current status of the server’s software raided disks.

~# cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md126 : active (auto-read-only) raid1 sdb2[1] sda2[0]
      1995776 blocks super 1.2 [2/2] [UU]

md127 : active raid1 sdb3[1] sda3[0]
      466718720 blocks super 1.2 [2/2] [UU]
      bitmap: 0/4 pages [0KB], 65536KB chunk

unused devices: <none>

To get a list of hard drives available to you for configuration run lsblk.

~# lsblk
sda         8:0    0 447.1G  0 disk
├─sda1      8:1    0     2M  0 part
├─sda2      8:2    0   1.9G  0 part
│ └─md127   9:127  0   1.9G  0 raid1 [SWAP]
└─sda3      8:3    0 445.2G  0 part
  └─md126   9:126  0 445.1G  0 raid1 /
sdb         8:16   0 447.1G  0 disk
├─sdb1      8:17   0     2M  0 part
├─sdb2      8:18   0   1.9G  0 part
│ └─md127   9:127  0   1.9G  0 raid1 [SWAP]
└─sdb3      8:19   0 445.2G  0 part
  └─md126   9:126  0 445.1G  0 raid1 /
sdc         8:32   0 447.1G  0 disk
sdd         8:48   0 447.1G  0 disk
sde         8:64   0 447.1G  0 disk
sdf         8:80   0 447.1G  0 disk

As you can see, there are four disks available, (sdc, sdd, sde, sdf), which we can use in a RAID.

Step 2: Preparing the Disks

Now that we know what drives to use, we can prepare them by using fdisk or parted, to create a partition table and change the partition type for our drives.

Note: You’ll need to repeat this for the four available drives (sdc, sdd, sde, sdf)

Bring up the disk utility with fdisk /dev/sdc. The command will bring up the command line interface. It works by typing the code of the option you’d like to select ( left side ) and confirming the selection by hitting the return/enter key.

~# fdisk /dev/sdc

Welcome to fdisk (util-linux 2.27.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.
Created a new DOS disklabel with disk identifier 0x6eac01f2.

Command (m for help): m


   a   toggle a bootable flag
   b   edit nested BSD disklabel
   c   toggle the dos compatibility flag

   d   delete a partition
   F   list free unpartitioned space
   l   list known partition types
   n   add a new partition
   p   print the partition table
   t   change a partition type
   v   verify the partition table
   i   print information about a partition

   m   print this menu
   u   change display/entry units
   x   extra functionality (experts only)

   I   load disk layout from sfdisk script file
   O   dump disk layout to sfdisk script file

  Save & Exit
   w   write table to disk and exit
   q   quit without saving changes

  Create a new label
   g   create a new empty GPT partition table
   G   create a new empty SGI (IRIX) partition table
   o   create a new empty DOS partition table
   s   create a new empty Sun partition table

Command (m for help):

Select n, “add a new partition” to create a new partition. We use the default recommendations here but feel free to configure as you see fit!

Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1):
First sector (2048-937703087, default 2048):
Last sector, +sectors or +size{K,M,G,T,P} (2048-937703087, default 937703087):

Created a new partition 1 of type 'Linux' and of size 447.1 GiB.

Select t, “change the partition type” to change the drives type. Typing L will show you all the the available types. We’re going to select Linux raid.

Command (m for help): t
Selected partition 1
Partition type (type L to list all types): L

 0  Empty           24  NEC DOS         81  Minix / old Lin bf  Solaris
 1  FAT12           27  Hidden NTFS Win 82  Linux swap / So c1  DRDOS/sec (FAT-
 2  XENIX root      39  Plan 9          83  Linux           c4  DRDOS/sec (FAT-
 3  XENIX usr       3c  PartitionMagic  84  OS/2 hidden or  c6  DRDOS/sec (FAT-
 4  FAT16 <32M      40  Venix 80286     85  Linux extended  c7  Syrinx
 5  Extended        41  PPC PReP Boot   86  NTFS volume set da  Non-FS data
 6  FAT16           42  SFS             87  NTFS volume set db  CP/M / CTOS / .
 7  HPFS/NTFS/exFAT 4d  QNX4.x          88  Linux plaintext de  Dell Utility
 8  AIX             4e  QNX4.x 2nd part 8e  Linux LVM       df  BootIt
 9  AIX bootable    4f  QNX4.x 3rd part 93  Amoeba          e1  DOS access
 a  OS/2 Boot Manag 50  OnTrack DM      94  Amoeba BBT      e3  DOS R/O
 b  W95 FAT32       51  OnTrack DM6 Aux 9f  BSD/OS          e4  SpeedStor
 c  W95 FAT32 (LBA) 52  CP/M            a0  IBM Thinkpad hi ea  Rufus alignment
 e  W95 FAT16 (LBA) 53  OnTrack DM6 Aux a5  FreeBSD         eb  BeOS fs
 f  W95 Ext'd (LBA) 54  OnTrackDM6      a6  OpenBSD         ee  GPT
10  OPUS            55  EZ-Drive        a7  NeXTSTEP        ef  EFI (FAT-12/16/
11  Hidden FAT12    56  Golden Bow      a8  Darwin UFS      f0  Linux/PA-RISC b
12  Compaq diagnost 5c  Priam Edisk     a9  NetBSD          f1  SpeedStor
14  Hidden FAT16 <3 61  SpeedStor       ab  Darwin boot     f4  SpeedStor
16  Hidden FAT16    63  GNU HURD or Sys af  HFS / HFS+      f2  DOS secondary
17  Hidden HPFS/NTF 64  Novell Netware  b7  BSDI fs         fb  VMware VMFS
18  AST SmartSleep  65  Novell Netware  b8  BSDI swap       fc  VMware VMKCORE
1b  Hidden W95 FAT3 70  DiskSecure Mult bb  Boot Wizard hid fd  Linux raid auto
1c  Hidden W95 FAT3 75  PC/IX           bc  Acronis FAT32 L fe  LANstep
1e  Hidden W95 FAT1 80  Old Minix       be  Solaris boot    ff  BBT

Don’t forget to write/save the changes you made!

Partition type (type L to list all types): fd
Changed type of partition 'Linux' to 'Linux raid autodetect'.

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

Do the same changes with the remaining 3 drives.

Step 3: Configuring the Software RAID 10

Confirm the partitions! Run lsblk to see your newly created partitions.

~# lsblk
sdc         8:32   0 447.1G  0 disk
└─sdc1      8:33   0 447.1G  0 part
sdd         8:48   0 447.1G  0 disk
└─sdd1      8:49   0 447.1G  0 part
sde         8:64   0 447.1G  0 disk
└─sde1      8:65   0 447.1G  0 part
sdf         8:80   0 447.1G  0 disk
└─sdf1      8:81   0 447.1G  0 part

The command we’ll be using to create RAID arrays is mdadm:

~# mdadm --create --verbose dev/name-of-your-drive --level=the-raid-configuration --raid-devices=the-<number-of-drives> dev/drive-1-name dev/drive-2-name

To configure RAID 10 run this command:

~# mdadm --create --verbose /dev/md0 --level=10 --raid-devices=4 /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1

You can check your RAID configurations by viewing the mdstat file with cat /proc/mdstat

~# cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid10 sdf1[3] sde1[2] sdd1[1] sdc1[0]
      937438208 blocks super 1.2 512K chunks 2 near-copies [4/4] [UUUU]
      [>....................]  resync =  0.1% (1232768/937438208) finish=75.9min speed=205461K/sec
      bitmap: 7/7 pages [28KB], 65536KB chunk

Now that we have a Raid 10 with our 4 drives, it's time to make a filesystem, and mount it.

Step 4: Creating and Mount the filesystem

Create a filesystem for the new md0 Raid

~# mkfs.ext4 -F /dev/md0

Next, create a mount point for it:

~# mkdir /mnt/raid

Mount the filesystem:

~# mount -t ext4 /dev/md0 /mnt/raid

And you can check it with the following:

~# df -h -x devtmpfs -x tmpfs
Filesystem      Size  Used Avail Use% Mounted on
/dev/md126      438G  856M  415G   1% /
/dev/md0        880G   72M  836G   1% /mnt/raid

Finally, we have to add the new filesystem mount options to the /etc/fstab file for automatic mounting at boot.

Here we will use the UUID rather than the /dev/md0 name.

~# blkid | grep md0
/dev/md0: UUID="d920df8a-d89e-4de6-8ce3-24507b17bc29" TYPE="ext4"

And we add it on the /etc/fstab file:

~# echo 'UUID="d920df8a-d89e-4de6-8ce3-24507b17bc29" /mnt/raid ext4 defaults 0 0' | tee -a /etc/fstab

If you want to test the fstab, you can simply unmount the raid with umount /mnt/raid and them use mount -a which will mount everything from the fstab file.

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