In a non-volatile memory system, such as flash memory, when selecting a block for write operation, the system selects blocks from a free block list (FBL). The memory circuits of non-volatile systems often experience cluster failures, where multiple blocks of a physical region are bad. If the free block list is loaded with blocks from a region having a cluster failure, this can result in multiple back to back write errors. To help avoid this situation, the blocks of a memory array are divided into physical zones and, when selecting blocks to replenish the free block list, blocks are chosen cyclically from the zones.