1. A method for snapshot management in a storage management system that comprises one or more snapshot-capable storage arrays hosting a plurality of logical unit numbers, the method comprising: executing a unified-snapshot job that generates at most one snapshot for a logical unit number in the plurality of logical unit numbers, regardless of the number of clients that store primary data to the respective logical unit number; wherein the executing of the unified-snapshot job comprises: discovering, by a storage manager, a first subclient of a first client and a second subclient of a second client which is distinct from the first client, wherein the first client generates first primary data that is stored to one or more logical unit numbers in the plurality of logical unit numbers, and wherein the first subclient represents a logical grouping of part of the first primary data, and wherein the second client generates second primary data that is stored to at least one of the one or more logical unit numbers storing the first primary data, and wherein the second subclient represents a logical grouping of part of the second primary data, discovering, by a media agent component of the storage management system, a first logical unit number in the plurality of logical unit numbers, wherein the first logical unit number comprises (i) data of the first subclient and (ii) data of the second subclient, instructing, by the media agent, a first storage array that hosts the first logical unit number to generate and store a first snapshot of the first logical unit number; and registering, by at least one of the media agent and the storage manager: (a) a first association between the generated first snapshot of the first logical unit number and the first subclient, and (b) a second association between the generated first snapshot of the first logical unit number and the second subclient.