Maintaining logically consistent backups using minimal data transfer. A backup, or snapshot, copy of original data is created and stored. A user designates data blocks that are to be backed up in a process of creating a subsequent snapshot copy of the data. Data blocks that are to be backed up might include those associated with active files having data of interest to the user. Data blocks that are not desired for backup might include, for example, swap files, printer buffers and temp files. The changes that have been made to the data blocks that have been designated for backup are applied to the snapshot copy after a specified time period has elapsed. Since only desired data blocks are backed up to the snapshot copy, memory, processing cycles and communication bandwidth are used more efficiently than if all data blocks were to be backed up to the snapshot copy.