Data storage device and method for low-latency power state transitions by having power islanding in a host memory buffer

A method comprising:

• performing the following in a host in communication with a data storage device, wherein the host comprises a host memory buffer:
• storing data received from the data storage in the host memory buffer;
• storing updates to the data in the host memory buffer, wherein some but not all of the updates are also stored in the data storage device;
• informing the data storage device that a first location in the host memory buffer will not be powered on during a low-power state;
• and
• receiving a command from the data storage device to, prior to entering the low-power state, flush a subset of the updates from the first location in the host memory buffer to a second location in the host memory buffer that will be powered on during the low-power mode, wherein the subset of updates is not stored in the data storage device.

A data storage device comprising:

• a volatile memory;
• a non-volatile memory;
• means for storing data in a host memory buffer in a host:
• means for maintaining dual copies of updates to the data in both the host memory buffer and the volatile memory in the data storage device until a number of updates exceeds a threshold after which updates are stored in the host memory buffer without storing copies of the updates in the volatile memory in the data storage device;
• means for receiving information from the host that a first area of the host memory buffer will not be powered on during a low-power state;
• means for identifying update(s) stored in the first area of the host memory buffer that do not have copies stored in the volatile memory in the data storage device;
• and
• means for flushing the identified update(s) from the first area of the host memory buffer to a second area of the host memory buffer that will be powered on during the low-power state.