1. A system comprising: a first cluster server, comprising a first memory and a first one or more processors, backed up by a second cluster server comprising a second memory and a second one or more processors configured to: retrieve a first metadata file from the first cluster server, wherein the first cluster server is different from the second cluster server, wherein the first metadata file comprises a first ordered list of block identifiers for data blocks, wherein each block identifier is used to access a data block stored on one of a first plurality of block servers, wherein each block identifier is a hash based on content of its corresponding data block, and wherein the first ordered list of block identifiers corresponds to a first plurality of volumes of client metadata stored on the first cluster server; retrieve a second metadata file from the second cluster server, wherein the second metadata file comprises a second ordered list of block identifiers for data blocks, wherein each block identifier is used to access a data block stored on one of a second plurality of block servers, wherein each block identifier is a hash based on content of its corresponding data block, and wherein the second ordered list of block identifiers corresponds to a second plurality of volumes of client metadata stored on the second cluster server; compare the first metadata file to the second metadata file to determine a difference list, wherein the difference list comprises block identifiers from the first ordered list that differ from block identifiers of the second ordered list; and send, to the first cluster server, a request for data blocks, wherein the request comprises the block identifiers from the difference list.