Method for remote asynchronous replication of volumes and apparatus therefor

A system for asynchronous volume replication, comprising:

• a first storage virtualization subsystem located on a first site, comprising a first controller and a first storage unit, wherein the first storage unit has a first volume and a first backup image;
• a second storage unit located on a second site, wherein the second storage unit has a second volume;
• and
• a host located on the first site and coupled with the first storage virtualization subsystem, wherein the host sends a Host IO request to the first volume of the first storage virtualization subsystem;
• wherein the first volume located on the first site and the second volume located on the second site form a mirroring pair in which the first volume has a first set of update information for recording the updated status information of each data block of the first volume and a first set of log information for recording the synchronous status information between the first volume and the second volume and the second volume has a second set of update information for recording the updated status information of each data block of the second volume and a second set of log information for recording the synchronous status information between the second volume and the first volume, and wherein at least a part of the first volume and a part of the second volume have once been in a synchronous status before forming the mirroring pair;
• wherein when the first controller of the first storage virtualization subsystem receives the Host IO request, a backup-on-write operation is executed, which comprises steps of:
• determining, according to the first set of update information and the first set of log information of the first volume and the second set of update information and the second set of log information of the second volume, whether an original data set of a first data block, which is to be written, of the first volume is the same as a data set of a second data block of the second volume, where the second data block corresponds to the first data block and the original data set of the first data block is not yet physically copied to the second volume;
• obtaining a determination result;
• not backing up the original data set to a first backup image located on the first site if the determination result shows that the original data set of the first data block of the first volume is the same as the data set of the second data block of the second volume;
• and
• backing up the original data set to the first backup image located on the first site if the determination result shows that the original data set of the first data block of the first volume is different from the data set of the second data block of the second volume;
• writing an updated data of the Host IO request into the first data block of the first volume by the first controller;
• and
• informing the host of completion of the Host IO request.