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16.4. Supported RAID conversions

RAID level conversions are supported between different configurations using specific mdadm commands, with disk requirements varying by the target RAID type.

You can convert from one RAID level to another. For example, you can convert from RAID10 to RAID5, but there is an intermediate step in between from RAID10 to RAID0, then to RAID5. See the following table for more supported RAID conversions:

Expand
RAID conversion levelsConversion stepsNotes

RAID level 0 to RAID level 4 

# mdadm --grow /dev/md0 --level=4 -n3 --add /dev/vdd

You need to add a disk to the MD array because it requires at least 3 disks.

RAID level 0 to RAID level 5 

# mdadm --grow /dev/md0 --level=5 -n3 --add /dev/vdd

You need to add a disk to the MD array because it requires at least 3 disks.

RAID level 0 to RAID level 10 

# mdadm --grow /dev/md0 --level 10 -n 4 --add /dev/vd[ef]

You need to add two extra disks to the MD array.

RAID level 1 to RAID level 0 

# mdadm --grow /dev/md0 -l0
 

RAID level 1 to RAID level 5 

# mdadm --grow /dev/md0 --level=5

You need to add 3 extra disks to the MD array.

RAID level 4 to RAID level 0 

# mdadm --grow /dev/md0 --level=0
 

RAID level 4 to RAID level 5 

# mdadm --grow /dev/md0 --level=5
 

RAID level 5 to RAID level 0 

# mdadm --grow /dev/md0 --level=0
 

RAID level 5 to RAID level 1 

# mdadm -CR /dev/md0 -l5 -n3 /dev/sd[abc] --assume-clean --size 1G


# mdadm -D /dev/md0 | grep Level


# mdadm -D /dev/md0 | grep "Used Dev Size"


# mdadm --grow /dev/md0 --array-size 1048576


# mdadm --grow -n 2 /dev/md0 --backup=internal


# mdadm --grow -l1 /dev/md0


# mdadm -D /dev/md0 | grep Level

The --size 1G option means 1 GB per disk, the final RAID5 data size is 2 GB.

Using --backup=internal creates a file named "internal" in the current directory.

RAID level 5 to RAID level 4 

# mdadm --grow /dev/md0 --level=4
 

RAID level 5 to RAID level 6 

# mdadm --grow /dev/md0 --level=6 --add /dev/vde
 

RAID level 5 to RAID level 10 

# mdadm --grow /dev/md0 --level=0 # mdadm --grow /dev/md0 --level=10 --add /dev/vde /dev/vdf

Converting RAID level 5 to RAID level 10 is a two step conversion:

  1. Convert to RAID level 0.
  2. Add two additional disks while converting to RAID10.

One of the RAID5 disks is removed after the conversion to RAID0.

RAID level 6 to RAID level 5 

# mdadm --grow /dev/md0 --level=5

One of the RAID6 disks is in spare status (for hot backup) in the new RAID5 array.

RAID level 10 to RAID level 0 

# mdadm --grow /dev/md0 --level=0

Two of RAID10 disks are removed from the new RAID0 array.

注意

Converting RAID5 to RAID0 and RAID4 is only possible with the ALGORITHM_PARITY_N layout.

After converting a RAID level, verify the conversion by using either the mdadm --detail /dev/md0 or cat /proc/mdstat command.

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