What erasure coding schemes are

When you configure the Erasure Coding profile for an ILM rule, you select an available erasure coding scheme based on how many Storage Nodes and sites make up the storage pool you plan to use. Erasure coding schemes control how many data fragments and how many parity fragments are created for each object.

The StorageGRID system uses the Reed-Solomon erasure coding algorithm. The algorithm slices an object into k data fragments and computes m parity fragments. The k + m = n fragments are spread across n Storage Nodes to provide data protection. An object can sustain up to m lost or corrupt fragments. k fragments are needed to retrieve or repair an object.

When configuring an Erasure Coding profile, confirm that the storage pool includes exactly one site or three or more sites. Do not use the default storage pool, All Storage Nodes, or a storage pool that includes the default site, All Sites.
Note: You cannot configure an Erasure Coding profile if the storage pool includes two sites.

Erasure coding schemes for storage pools containing three or more sites

The following table lists the erasure coding schemes currently supported by StorageGRID for storage pools that include three or more sites. It specifies the recommended number of sites and Storage Nodes for each scheme. The supported erasure coding schemes are designed to provide site loss protection. One site can be lost, and the object will still be accessible.
Erasure coding scheme

(k + m)

Minimum number of deployed sites Recommended number of Storage Nodes at each site Total recommended number of Storage Nodes Site loss protection?
4+2 3 3* 9 Yes
6+2 4 3* 12 Yes
8+2 5 3* 15 Yes
6+3 3 4 12 Yes
9+3 4 4 16 Yes
2+1 3 3* 9 Yes
4+1 5 3* 15 Yes
6+1 7 3* 21 Yes

* At minimum, each site requires three Storage Nodes.

Additional erasure coding schemes are available. Contact your account manager.

When deciding which erasure coding scheme to use, you should balance fault tolerance (achieved by having more parity segments) against the network traffic requirements for repairs (more fragments equals more network traffic). For example, when deciding between a 4+2 scheme and 6+3 scheme, select the 6+3 scheme if additional parity and fault tolerance are required. Select the 4+2 scheme if network resources are constrained to reduce network usage during node repairs.
Note: If you are unsure of which scheme to use, select 4+2 or 6+3, or contact support. In general, you should avoid using the m+1 schemes unless your application does not require a high degree of fault tolerance.

Erasure coding schemes for one-site storage pools

Erasure coding is well suited for single-site deployments that require efficient data protection with only a single erasure-coded copy rather than multiple replicated copies. A storage pool that includes only one site supports all of the erasure coding schemes listed in the previous table, assuming that the site includes an adequate number of Storage Nodes. For example, the 2+1 erasure coding scheme requires a storage pool with three or more Storage Nodes, while the 6+3 scheme requires a storage pool with at least nine Storage Nodes.