Systems, methods, and machine-readable media for controlling an upload of a block of data associated with an upload command are described. In certain aspects, an interface module may be configured to obtain a cryptographic checksum for the block of data associated with the upload command. A checksum module may configured to compare the cryptographic checksum for the block of data associated with the upload command to a cryptographic checksum in an index storing cryptographic checksums identifying blocks of data previously uploaded to a server. If the cryptographic checksum for the block of data associated with the upload command matches the cryptographic checksum in the index, an upload module may be configured to cancel the upload of the block of data associated with the upload command.