Tracking incremental changes in a mass storage system

In a computer system having a mass storage device that stores data in a plurality of data blocks and has access to a data storage location that contains a snapshot copy of the data, a method of tracking incremental changes of the plurality of data blocks in the mass storage device, the method comprising:

• at a first time, initiating the creation of a snapshot copy of data in a plurality of data blocks of a mass storage device;
• during a time period between the first time and a second time,
• identifying a write request to a first data block;
• identifying whether the first data block of the mass storage device is a protected or unprotected data block;
• if the first data block is a protected data block, copying original data of the first data block to a preservation memory;
• if the first data block is an unprotected data block, not copying original data of the first data block to the preservation memory;
• and
• overwriting the original data of the first data block with new data included in the write request;
• at the second time, initiating an update of the snapshot copy by transmitting to the data storage location that contains the snapshot copy a copy of the new data;
• and
• maintaining the original data of the first data block in the preservation memory for a period of time after the update of the snapshot copy.

A computer program product for implementing, in a computer system having a mass storage device that stores data in a plurality of data blocks and has access to a data storage location that contains a snapshot copy of the data, a method of tracking incremental changes of the plurality of data blocks in the mass storage device, wherein the computer program product comprises a computer-readable medium carrying computer-executable instructions for implementing the method, wherein the computer-executable instructions, when executed by the computer system, cause the computer system to perform the acts of:

• identify a write request to a first data block of a mass storage device;
• identify whether the first data block of the mass storage device is a protected or unprotected data block;
• if the first data block is a protected data block, copy original data of the first data block to a preservation memory;
• if the first data block is an unprotected data block, not copying original data of the first data block to the preservation memory;
• overwrite the original data of the first data block with new data included in the write request;
• use the new data of the first data block to create a snapshot;
• and
• maintain the preservation memory for a period of time after the creation of the snapshot.