Erasure Coding

Erasure code is a mathematical algorithm to reconstruct missing or corrupted data. DC/OS Minio specifies two storage classes to define an Erasure Coding Scheme: STANDARD Storage class and REDUCED_REDUNDANCY Storage class.

Allowed values for STANDARD storage class

STANDARD storage class implies more parity than REDUCED_REDUNDANCY class. STANDARD parity disks should be

• Greater than or equal to 2, if REDUCED_REDUNDANCY parity is not set.
• Greater than REDUCED_REDUNDANCY parity, if it is set.

Parity blocks can not be higher than data blocks, so STANDARD storage class parity can not be higher than N/2. (N = total number of disks)

Default value for STANDARD storage class is N/2 (N = the total number of drives).

Allowed values for REDUCED_REDUNDANCY storage class

Default value for REDUCED_REDUNDANCY storage class is 2.

REDUCED_REDUNDANCY implies lesser parity than STANDARD class. REDUCED_REDUNDANCY parity disks should be

• Less than N/2, if STANDARD parity is not set.
• Less than STANDARD Parity, if it is set.

Parity below 2 is not recommended, therefore a REDUCED_REDUNDANCY storage class is not supported for an erasure coding setup for four disks.