Method for maintaining high performance while preserving relative write I/O ordering for a semi-synchronous remote replication solution

A method of providing remote replication of data comprising the steps of:

• receiving data including dependent and independent writes;
• storing each write received in a queue;
• assigning a sequence number to each write, the sequence number indicating a time interval in which the write begins;
• assigning a horizon number to each write request, the horizon number indicating a time interval in which a first write that started at a particular sequence number ends;
• removing a write from the queue and causing it to be stored on a storage device and assigning the horizon number associated with the write as a replication number;
• removing another write from the queue and causing it to be stored on the storage device if the sequence number associated with the write is less than the replication number;
• and
• also assigning the horizon number to a previous write if no writes ended in the previous write's sequence number interval.

A program product comprising a computer readable medium having embodied therein a computer program for storing data, the computer program comprising:

• logic for receiving a stream of data including independent streams of dependent writes;
• logic for discerning dependent writes from independent writes;
• and
• logic for causing writes from independent streams to be stored on a storage device in parallel until a dependent write in a stream needs to be stored on the storage device;
• wherein the logic for discerning comprises:
• logic for assigning a sequence number to each write, the sequence number indicating a time interval in which the write begins;
• and
• logic for assigning a horizon number to each write request, the horizon number indicating a time interval in which a first write that started at a particular sequence number ends;
• wherein the logic for causing comprises:
• logic for causing a write to be stored on a storage device and assigning the horizon number associated with the write as a replication number;
• logic for causing another write to be stored on the storage device if the sequence number associated with the write is less than the replication number;
• and
• logic for waiting until all outstanding writes complete if the sequence number associated with the write is greater than the replication number.

A program product comprising a computer readable medium having embodied therein a computer program for storing data, the computer program comprising:

• logic for receiving data including dependent and independent writes;
• logic for storing each write received in a queue;
• logic for assigning a sequence number to each write, the sequence number indicating a time interval in which the write begins;
• logic for assigning a horizon number to each write request, the horizon number indicating a time interval in which a first write that started at a particular sequence number ends;
• logic for removing a write from the queue and causing it to be stored on a storage device and assigning the horizon number associated with the write as a replication number;
• logic for removing another write from the queue and causing it to be stored on the storage device if the sequence number associated with the write is less than the replication number;
• and
• logic for also assigning the horizon number to a previous write if no writes ended in the previous write's sequence number interval.

Apparatus in a storage system for providing remote replication of data, the apparatus comprising:

• logic for receiving a stream of data including independent streams of dependent writes;
• logic for discerning dependent writes from independent writes;
• and
• logic for causing writes from independent streams to be stored on a storage device in parallel until a dependent write in a stream needs to be stored on the storage device;
• wherein the logic for discerning comprises:
• logic for assigning a sequence number to each write, the sequence number indicating a time interval in which the write begins;
• and
• logic for assigning a horizon number to each write request, the horizon number indicating a time interval in which a first write that started at a particular sequence number ends;
• wherein the logic for causing comprises:
• logic for causing a write to be stored on a storage device and assigning the horizon number associated with the write as a replication number;
• logic for causing another write to be stored on the storage device if the sequence number associated with the write is less than the replication number;
• and
• logic for waiting until all outstanding writes complete if the sequence number associated with the write is greater than the replication number.

Apparatus in a storage system for providing remote replication of data, the apparatus comprising:

• logic for receiving data including dependent and independent writes;
• logic for storing each write received in a queue;
• logic for assigning a sequence number to each write, the sequence number indicating a time interval in which the write begins;
• logic for assigning a horizon number to each write request, the horizon number indicating a time interval in which a first write that started at a particular sequence number ends;
• logic for removing a write from the queue and causing it to be stored on a storage device and assigning the horizon number associated with the write as a replication number;
• logic for removing another write from the queue and causing it to be stored on the storage device if the sequence number associated with the write is less than the replication number;
• and
• logic for also assigning the horizon number to a previous write if no writes ended in the previous write's sequence number interval.