Methods and apparatuses are disclosed, such as those including a block of memory cells that includes strings of charge storage devices. Each of the strings may comprise a plurality of charge storage devices formed in a plurality of tiers. The apparatus may comprise a plurality of access lines shared by the strings. Each of the plurality of access lines may be coupled to the charge storage devices corresponding to a respective tier of the plurality of tiers. The apparatus may comprise a plurality of sub-sources associated with the strings. Each of the plurality of sub-sources may be coupled to a source select gate of each string of a respective subset of a plurality of subsets of the strings, and each sub-source may be independently selectable from other sub-sources to select the strings of its respective subset independently of other strings corresponding to other subsets.