A storage system according to certain embodiments includes a repository of client-side data block signature information representative of a set of data blocks stored in a primary storage subsystem. In some cases, the system sources data blocks for secondary copy and restore operations from the primary storage subsystem instead of the secondary storage subsystem. Where multiple primary storage components (e.g., multiple client computing devices) contain copies of a data blocks involved in a secondary copy or restore operation, the system can decide which client to source the data block from based on sourcing criteria.