Optimizing spare capacity and spare distribution

Configuring spare sections in a system having a plurality of devices and having a plurality of erasure encoding groups, each of the devices having a plurality of sections and each of the groups having a plurality of members located on the sections of the devices, includes configuring the system to have a plurality of erasure encoding groups with no spare sections, ordering the groups according to desirability of converting members of each of the groups into spare sections, converting members of a subset of the groups into spare sections according to ordering of the groups, and determining if the spare sections for the system provide sufficient coverage for the system in response to failure of each of the devices. The erasure encoding may be a RAID encoding.