Synchronous and asymmetric asynchronous active-active-active data access

A method to provide synchronous and asymmetric active-active-active access to a first storage volume using a global cache coupled to a first, second and third virtual storage volumes comprising:

• replicating asynchronously the first storage volume at a first site to a second storage volume at a second site;
• mirroring the first storage volume with a third storage volume at a third site, either one of the first storage volume or the third storage volume having primary storage functionality;
• virtualizing the first storage volume with the first virtual storage volume;
• virtualizing the second storage volume with the second virtual storage volume;
• virtualizing the third storage volume with the third virtual storage volume;
• and
• transferring the primary storage functionality from the first site and the third site to the second site,
• wherein the transferring comprising:
• notifying the global cache of an attempt to transfer primary storage functionality from the first site to the second site;
• suspending I/O requests to the first storage volume;
• transferring lagging data to the second storage volume;
• and
• starting I/O requests at the second storage volume as having primary storage functionality if the secondary storage volume mirrors the first storage and the third volume before a predetermined amount of time elapses;
• and
• allowing I/O requests to proceed to the first storage volume and the third storage volume if the secondary storage volume does not mirror the first storage volume and third storage volume before a predetermined amount of time elapses.

An apparatus, comprising:

• electronic hardware circuitry to provide synchronous and asymmetric active-active-active access to a first storage volume using a global cache coupled to a first, second and third virtual storage volumes, the circuitry configured to:
• replicate asynchronously the first storage volume at a first site to a second storage volume at a second site;
• mirror the first storage volume with a third storage volume at a third site, either one of the first storage volume or the third storage volume having primary storage functionality;
• virtualize the first storage volume with the first virtual storage volume;
• virtualize the second storage volume with the second virtual storage volume;
• virtualize the third storage volume with the third virtual storage volume;
• mark locations which are marked as different between the second storage volume and the third storage volume as having a phase to enable reads to be served locally from the third site;
• receive a request to read a location on the first storage volume at the second site;
• read the location at the first storage volume or the third storage volume if the global cache has a phase value for the location;
• read the location at the second storage volume if the global cache does not have a phase value for the location;
• and
• tracking locations in the secondary storage volume that do not mirror the first storage volume,
• wherein the circuitry configured to track comprises circuitry configured to:
• for every write I/O request, track a phase for each location on the first storage volume, the second storage volume and the third storage volume;
• periodically change the phase;
• for every I/O write request written, add a phase value indicating the phase to the I/O write request;
• notify the global cache of the last applied phase for each location;
• and
• clear phase values for all locations at the second storage volume more than one phase old.

An apparatus, comprising:

• electronic hardware circuitry to provide synchronous and asymmetric active-active-active access to a first storage volume using a global cache coupled to a first, second and third virtual storage volumes, the circuitry configured to:
• replicate asynchronously the first storage volume at a first site to a second storage volume at a second site;
• mirror the first storage volume with a third storage volume at a third site, either one of the first storage volume or the third storage volume having primary storage functionality;
• virtualize the first storage volume with the first virtual storage volume;
• virtualize the second storage volume with the second virtual storage volume;
• virtualize the third storage volume with the third virtual storage volume;
• and
• transfer the primary storage functionality from the first site and the third site to the second site,
• wherein the circuitry configured to transfer comprises circuitry configured to:
• notify the global cache of an attempt to transfer primary storage functionality from the first site to the second site;
• suspend I/O requests to the first storage volume;
• transfer lagging data to the second storage volume;
• and
• start I/O requests at the second storage volume as having primary storage functionality if the secondary storage volume mirrors the first storage and the third volume before a predetermined amount of time elapses;
• and
• allow I/O requests to proceed to the first storage volume and the third storage volume if the secondary storage volume does not mirror the first storage volume and third storage volume before a predetermined amount of time elapses.

An article comprising:

• a non-transitory computer-readable medium that stores computer-executable instructions to provide asymmetric active-active access to a first storage volume using a global cache coupled to a first and second virtual storage volumes, the instructions causing a machine to:
• replicate asynchronously the first storage volume at a first site to a second storage volume at a second site;
• mirror the first storage volume with a third storage volume at a third site, either one of the first storage volume or the third storage volume having primary storage functionality;
• virtualize the first storage volume with the first virtual storage volume;
• virtualize the second storage volume with the second virtual storage volume;
• virtualize the third storage volume with the third virtual storage volume;
• mark locations which are marked as different between the second storage volume and the third storage volume as having a phase to enable reads to be served locally from the third site,
• receive a request to read a location on the first storage volume at the second site;
• read the location at the first storage volume or the third storage volume if the global cache has a phase value for the location;
• read the location at the second storage volume if the global cache does not have a phase value for the location;
• and
• tracking locations in the secondary storage volume that do not mirror the first storage volume,
• wherein the instructions causing the machine to track comprises instructions causing the machine to:
• for every write I/O request, track a phase for each location on the first storage volume, the second storage volume and the third storage volume;
• periodically change the phase;
• for every I/O write request written, add a phase value indicating the phase to the I/O write request;
• notify the global cache of the last applied phase for each location;
• and
• clear phase values for all locations at the second storage volume more than one phase old.

An article comprising:

• a non-transitory computer-readable medium that stores computer-executable instructions to provide asymmetric active-active access to a first storage volume using a global cache coupled to a first and second virtual storage volumes, the instructions causing a machine to:
• replicate asynchronously the first storage volume at a first site to a second storage volume at a second site;
• mirror the first storage volume with a third storage volume at a third site, either one of the first storage volume or the third storage volume having primary storage functionality;
• virtualize the first storage volume with the first virtual storage volume;
• virtualize the second storage volume with the second virtual storage volume;
• virtualize the third storage volume with the third virtual storage volume;
• and
• transfer the primary storage functionality from the first site and the third site to the second site,
• wherein the instructions causing the machine to transfer comprises instructions causing the machine to:
• notify the global cache of an attempt to transfer primary storage functionality from the first site to the second site;
• suspend I/O requests to the first storage volume;
• transfer lagging data to the second storage volume;
• and
• start I/O requests at the second storage volume as having primary storage functionality if the secondary storage volume mirrors the first storage and the third volume before a predetermined amount of time elapses;
• and
• allow I/O requests to proceed to the first storage volume and the third storage volume if the secondary storage volume does not mirror the first storage volume and third storage volume before a predetermined amount of time elapses.