Declustered arrays

A declustered array is a subset of the physical disks (pdisks) in a recovery group across which data, redundancy information, and spare space are declustered. The number of disks in a declustered array is determined by the RAID code-width of the vdisks that is housed in the declustered array. For more information, see Virtual disks. There can be one or more declustered arrays per recovery group. Figure 1 illustrates a storage JBOD with two recovery groups, each with four declustered arrays.

A declustered array can hold one or more vdisks. Since redundancy codes are associated with vdisks, a declustered array can simultaneously contain both Reed-Solomon and replicated vdisks.

If the storage JBOD supports multiple disks that are physically mounted together on removable carriers, removal of a carrier temporarily disables access to all the disks in the carrier. Thus, pdisks on the same carrier must not be in the same declustered array, as vdisk redundancy protection would be weakened upon carrier removal.

Declustered arrays are normally created at recovery group creation time but new ones can be created or existing ones that are grown by adding pdisks later.

Figure 1. Example of declustered arrays and recovery groups in storage JBOD. This figure shows a storage JBOD with two recovery groups, each recovery group with four declustered arrays, and each declustered array with five disks.
Example of declustered arrays and recovery groups in storage JBOD.