The following software RAID levels are commonly implemented with Oracle Linux:

Linear RAID (spanning)

Combines drives as a larger virtual drive. This level provides no data redundancy nor performance benefit. Resilience decreases because the failure of a single drive renders the array unusable.

RAID-0 (striping)

Increases performance but doesn't provide data redundancy. Data is broken down into units (stripes) and written to all the drives in the array. Resilience decreases because the failure of a single drive renders the array unusable.

RAID 0+1 (mirroring of striped disks)

Combines RAID-0 and RAID-1 by mirroring a striped array to provide both increased performance and data redundancy. Failure of a single disk causes one of the mirrors to be unusable until you replace the disk and repopulate it with data. Resilience is degraded while only a single mirror remains available. RAID 0+1 is usually as expensive as or slightly more expensive than RAID-1.

RAID-1 (mirroring)

Provides data redundancy and resilience by writing identical data to each drive in the array. If one drive fails, a mirror can satisfy I/O requests. Mirroring is an expensive solution because the same information is written to all of the disks in the array.

RAID 1+0 (striping of mirrored disks or RAID-10)

Combines RAID-0 and RAID-1 by striping a mirrored array to provide both increased performance and data redundancy. Failure of a single disk causes part of one mirror to be unusable until you replace the disk and repopulate it with data. Resilience is degraded while only a single mirror retains a complete copy of the data. RAID 1+0 is typically as expensive as or slightly more expensive than RAID-1.

RAID-5 (striping with distributed parity)

Increases read performance by using striping and provides data redundancy. The parity is distributed across all the drives in an array, but it doesn't take up as much space as a complete mirror. Write performance is reduced to some extent as a result of the need to calculate parity information and to write the information in addition to the data. If one disk in the array fails, the parity information is used to reconstruct data to satisfy I/O requests. In this mode, read performance and resilience are degraded until you replace the failed drive and repopulate the new drive with data and parity information. RAID-5 is intermediate in expense between RAID-0 and RAID-1.

RAID-6 (Striping with double distributed parity)

A more resilient variant of RAID-5 that can recover from the loss of two drives in an array. The double parity is distributed across all the drives in an array, to ensure redundancy at the expense of taking up more space than RAID-5. For example, in an array of four disks, if two disks in the array fails, the parity information is used to reconstruct data. Usable disks are the number of disks minus two. RAID-6 is used when data redundancy and resilience are important, but performance is not. RAID-6 is intermediate in expense between RAID-5 and RAID-1.

1. Run the mdadm command to create the MD RAID device as follows:

   sudo mdadm --create md_device --level=RAID_level [options] --raid-devices=Ndevices
   

   md_device

   Name of the RAID device, for example, /dev/md0.

   RAID_level

   Level number of the RAID to create, for example, 5 for a RAID-5 configuration.

   --raid-devices=N

   Number of devices to become part of the RAID configuration.

   devices

   Devices to be configured as RAID, for example, /dev/sd[bcd] for 3 devices for the RAID configuration.

   The devices you list must total to the number you specified for --raid-devices.

   This example creates a RAID-5 device /dev/md1 from /dev/sdb, /dev/sdc, and dev/sdd:

   sudo mdadm --create /dev/md1 --level=5 -raid-devices=3 /dev/sd[bcd]

   The previous example creates a RAID-5 device /dev/md1 out of 3 devices. We can use 4 devices where one device is configured as a spare for expansion, reconfiguration, or replacement of failed drives:

   sudo mdadm --create /dev/md1 --level=5 -raid-devices=3 --spare-devices=1 /dev/sd[bcde]

2. (Optional) Add the RAID configuration to /etc/mdadm.conf:

   sudo mdadm --examine --scan >> /etc/mdadm.conf

   Based on the configuration file, mdadm assembles the arrays at boot time.

   For example, the following entries define the devices and arrays that correspond to /dev/md0 and /dev/md1:

   DEVICE /dev/sd[c-g]
   ARRAY /dev/md0 devices=/dev/sdf,/dev/sdg
   ARRAY /dev/md1 spares=1 devices=/dev/sdb,/dev/sdc,/dev/sdd,/dev/sde

   For more examples, see the sample configuration file /usr/share/doc/mdadm-3.2.1/mdadm.conf-example.

An MD RAID device is used in the same way as any physical storage device. For example, the RAID device can be configured as an LVM physical volume, a file system, a swap partition, an Automatic Storage Management (ASM) disk, or a raw device.

To check the status of the MD RAID devices, view /proc/mdstat:

cat /proc/mdstat

Personalities : [raid1]
mdo : active raid1 sdg[1] sdf[0]

To display a summary or detailed information about MD RAID devices, use the --query or --detail option, respectively, with mdadm.

For more information, see the md(4), mdadm(8), and mdadm.conf(5) manual pages.

1. Ensure that you have created a sufficient number of physical volumes in a volume group to accommodate your LVM RAID logical volume requirements. For more information about creating physical volumes and volume groups, see Working With Logical Volume Manager.

2. Review the raid_fault_policy value in the /etc/lvm/lvm.conf file that specifies how a RAID instance that uses redundant devices reacts to a drive failure. The default value is "warn" which indicates that RAID is configured to log a warning in the system logs. This means that in the event of a device failure, manual action is required to replace the failed device.
3. Run the lvcreate command to create the LVM RAID device. See the following sections for examples:

   • RAID Level 0 (Striping) LVM Examples
   • RAID Level 1 (Mirroring) LVM Examples
   • RAID Level 5 (Striping with Distributed Parity) LVM Examples
   • RAID Level 6 (Striping with Double Distributed Parity) LVM Examples
   • RAID Level 10 (Striping of Mirrored Disks) LVM Examples
4. Create the filesystem you want on your device. For example, the following command creates an ext4 file system on a RAID 6 logical volume.

   sudo mkfs.ext4 /dev/myvg/mylvraid6
   mke2fs 1.46.2 (28-Feb-2021)
   Creating filesystem with 264192 4k blocks and 66096 inodes
   Filesystem UUID: 05a78be5-8a8a-44ee-9f3f-1c4764c957e8
   Superblock backups stored on blocks: 
   	32768, 98304, 163840, 229376
   

5. Consider persisting the logical volume by editing your /etc/fstab file. For example, adding the following line that includes the UUID created in the previous step ensures that the logical volume is remounted after a reboot.

   UUID=05a78be5-8a8a-44ee-9f3f-1c4764c957e8 /mnt ext4 defaults 0 0
   

   For more information about using UUIDs with the /etc/fstab file, see Automatic Device Mappings for Partitions and File Systems .

6. In the event that a device failure occurs for LVM RAID levels 5, 6, and 10, ensure that you have a replacement physical volume attached to the volume group that contains the failed RAID device, and do one of the following:

   • Use the following command to switch to a random spare physical volume present in the volume group:

     sudo lvconvert --repair volume_group/logical_volume

     In the previous example, volume_group is the volume group and logical_volume is the LVM RAID logical volume.

   • Use the following command to switch to a specific physical volume present in the volume group:

     sudo lvconvert --repair volume_group/logical_volume physical_volume

     In the previous example, physical_volume is the specific volume you want to replace the failed physical volume with. For example, /dev/sdb1.