Systems and methods of asynchronous data replication

1. A system of asynchronous data replication, comprising:

a primary host asynchronously transmitting write commands and sync commands, wherein each write command has a data set ID and a sequence number and each sync command has a data set ID and a sequence number; and

a secondary host, coupled to the primary host, tracking receipt of the write and sync commands and after receipt of the write and sync commands, writing the data of the write commands to storage coupled to the secondary host.

2. The system of claim 1 , further comprising a data structure at the secondary host for tracking receipt of the write and sync commands.

3. The system of claim 2 , wherein the data structure includes a flag to indicate when the write commands and the sync command of a data set are received at the secondary host.

4. The system of claim 3 , wherein the secondary host writes the data set to the storage after a temporary failure of the secondary host if the flag indicates that the write and sync commands of the date set were received.

5. A system of asynchronous data replication, comprising:

a primary host asynchronously transmitting write and sync commands for a first data set and a second data set; and

a secondary host, coupled to the primary host, receiving and writing the write and sync commands to a storage, wherein the primary host transmits write and sync commands for the second data set before the secondary host acknowledges the first data set was written to the storage.

6. A system of asynchronous data replication, comprising:

a primary host asynchronously transmitting write commands and blocks over a network without waiting to complete a data set with a sync command; and

secondary host coupled to the network receiving the write commands, the blocks, and the sync command in any order, wherein the secondary host writes the data set to a storage coupled to the secondary host.

7. A system of asynchronous data replication, comprising:

a primary host receiving write commands from an application, generating sync commands, and transmitting the write and sync commands over a network asynchronously and independently from one or more data sets; and

a secondary host, coupled to the network, receiving the write and sync commands out of order and writing the data sets in order to a storage coupled to the secondary host.

8. A method of data replication, comprising the steps of:

transmitting a data set from a primary host to a secondary host wherein the secondary host includes a data structure with a complete flag;

writing the data set to a target VLUN at the secondary host;

setting the complete flag=yes once the data set is written to the target VLUN at the secondary host; and

writing the data set to a source VLUN at the secondary host only if the complete flag=yes to protect the integrity of the source VLUN at the secondary host.

9. A method of data replication when a secondary host falls comprising the steps of:

transmitting a data set from a primary host to the secondary hoot wherein the secondary host includes a data structure with a complete flag;

writing the data set to a target VLUN at the secondary host;

setting the complete flag=yes only if the data set is written to the target VLUN at the secondary host;

retransmitting the data set from the primary host to the secondary host if the secondary host fails and the complete flag=no, which indicates the data set was not written to the target VLUN; and

writing the data set to a source VLUN at the secondary host.

10. A method of data replication comprising the steps of:

transmitting a data set from a primary host to a secondary host wherein the secondary host includes a data structure with a complete flag;

writing part of the data set to a target VLUN at the secondary host;

resuming operation of the secondary host after a failure;

erasing the part of the data set written to the target VLUN at the secondary host;

retransmitting the data set from the primary host to the secondary host;

writing the data set to the target VLUN at the secondary host;

setting the complete flag=yes once the data set is written to the target VLUN at the secondary host; and

writing the data set to a source VLUN at the secondary host.