Use the resume and time options of the reorg command when reorganizing an entire table would take too long and interfere with other database activities. time allows you to run a reorg for a specified length of time. resume allows you to start a reorg at the point in a table where the previous reorg finished. In combination, the two options allow you to reorganize a large table by running a series of partial reorganizations (for example, during offhours).
resume and time are not available with reorg rebuild.