Efficiently providing virtual machine reference points

A computer system comprising the following:

• one or more processors;
• and
• one or more computer-readable storage media having stored thereon computer-executable instructions that are executable by the one or more processors to cause the computer system to perform at least the following:
• maintain a plurality of data storage identifiers that identify changed data blocks of a plurality of data blocks of a data storage corresponding to a virtual machine, wherein data storage identifiers are advanced at discrete points in time based at least on corresponding data blocks having been written to since a prior discrete point in time;
• access a stable virtual machine checkpoint comprising a restorable image of a virtual machine at a point in time, and that stores a representation of data of at least one of the plurality of data blocks of the data storage as it existed at the point in time;
• convert the virtual machine checkpoint to a virtual machine reference point comprising a representation of the virtual machine at the point in time, including:
• querying the data storage to determine at least one data storage identifier corresponding to the at least one data block of the virtual machine checkpoint at the point in time;
• storing the determined at least one data storage identifier as a part of the virtual machine reference point;
• and
• subsequent to converting the virtual machine checkpoint to the virtual machine reference point, use the virtual machine reference point to identify one or more changes in the plurality of data blocks of the data storage since the point in time, including identifying that the at least one data storage identifier corresponding to the at least one data block has been advanced since the point in time.

A computer program product comprising one or more hardware storage devices having stored thereon computer-executable instructions that are executable by one or more processors to cause a computer system to perform at least the following:

• maintain a plurality of data storage identifiers that identify changed data blocks of a plurality of data blocks of a data storage corresponding to a virtual machine, wherein data storage identifiers are advanced at discrete points in time based at least on corresponding data blocks having been written to since a prior discrete point in time;
• access a stable virtual machine checkpoint comprising a restorable image of a virtual machine at a point in time, and that stores a representation of data of at least one of the plurality of data blocks of the data storage as it existed at the point in time;
• convert the virtual machine checkpoint to a virtual machine reference point comprising a representation of the virtual machine at the point in time, including:
• querying the data storage to determine at least one data storage identifier corresponding to the at least one data block of the virtual machine checkpoint at the point in time;
• storing the determined at least one data storage identifier as a part of the virtual machine reference point;
• and
• subsequent to converting the virtual machine checkpoint to the virtual machine reference point, use the virtual machine reference point to identify one or more changes in the plurality of data blocks of the data storage since the point in time, including identifying that the at least one data storage identifier corresponding to the at least one data block has been advanced since the point in time.