LIGHTWEIGHT SYNCHRONIZATION OF MIRRORED DISKS

• US 20140181015A1
• Filed: 12/21/2012
• Published: 06/26/2014
• Est. Priority Date: 12/21/2012
• Status: Active Grant

• Current Assignee: Red Hat, Inc. (International Business Machines Corporation)
• Original Assignee: Red Hat, Inc. (International Business Machines Corporation)
• Inventors: Bonzini, Paolo
• Granted Patent: US 10,162,873 B2
• Time in Patent Office: Days
• US Class Current: 707/613
• CPC Class Codes: G06F 16/273 Asynchronous replication or reconciliation

Abstract

In a process for migrating a virtual machine'"'"'s storage from a source disk to a destination disk, during a steady state (i.e., wherein the contents of the virtual machine stored on the source disk and the destination disk are equal), a virtual machine monitor receives a set of write requests from a guest operating system (“guest”) of the virtual machine, provides confirmation of the completion of the set of writes to the source disk, and asynchronously replicates the set of write requests to the destination disk. Upon receipt of a flush request from the guest, the virtual machine monitor confirms completion of the flushing of the destination disk following replication of the write requests to the destination disk. Upon receipt of a switch request from a virtual machine manager, the virtual machine monitor switches the virtual machine to the destination disk and issues subsequent write requests to the destination disk.

Claims

1. A method comprising:

identifying, by the virtual machine monitor, a steady state wherein contents associated with a virtual machine stored on a source disk and a destination disk are equal;

receiving a set of write requests comprising data from a guest operating system of the virtual machine;

providing confirmation of a completion of the set of writes to the source disk;

asynchronously replicating the set of write requests to the destination disk;

receiving a flush request from the guest operating system of the virtual machine;

providing, to the guest operating system, confirmation of completion of a flush of the destination disk following replication of the set of write requests to the destination disk and writing of the data to persistent storage of the destination disk;

receiving a switch request from the virtual machine manager; and

switching the virtual machine to the destination disk and issuing subsequent write requests to the destination disk.

2. The method of claim 1, further comprising reporting to a virtual machine manager, by the virtual machine monitor, entry into the steady state.

3. The method of claim 1, wherein identifying the steady state further comprises:

maintaining a dirty bitmap to record one or more disk sectors that have been written to on the source disk but not the destination disk; and

emptying the dirty bitmap.

4. The method of claim 1, further comprising operating in a synchronization phase prior to steady state, wherein the synchronization phase comprises migrating the contents of the source disk to the destination disk.

5. The method of claim 4, further comprising entering the synchronization phase in response to at least one of receiving a request from the virtual machine manager or detecting an error in the replication of the set of write requests to the destination disk.

6. The method of claim 4, wherein the source disk is divided into a base image and an overlay image and only contents of the overlay image are migrated to the destination disk during the synchronization phase.

7. The method of claim 1, further comprising delaying processing of a write request to the source disk for a set period of time upon determining the contents stored on the source disk and the destination disk are equal.

8. A non-transitory computer readable storage medium including instructions that, when executed by a processing device, cause the processing device to perform operations comprising:

identifying, by a virtual machine monitor executed by the processing device, a steady state wherein contents associated with a virtual machine stored on a source disk and a destination disk are equal;

receiving, by the virtual machine monitor, a set of write requests comprising data from a guest operating system of the virtual machine;

providing confirmation of a completion of the set of writes to the source disk;

asynchronously replicating the set of write requests to the destination disk;

receiving a flush request from the guest operating system of the virtual machine;

providing, to the guest operating system, confirmation of completion of a flush of the destination disk following replication of the set of write requests to the destination disk and writing of the data to persistent storage of the destination disk;

receiving a switch request from a virtual machine manager; and

switching the virtual machine to the destination disk and issuing subsequent write requests to the destination disk.

9. The non-transitory computer readable storage medium of claim 8, further comprising reporting to a virtual machine manager, by the virtual machine monitor, entry into the steady state.

10. The non-transitory computer readable storage medium of claim 8, wherein identifying the steady state further comprises:

maintaining a dirty bitmap to record one or more disk sectors that have been written to on the source disk but not the destination disk; and

emptying the dirty bitmap.

11. The non-transitory computer readable storage medium of claim 8, further comprising operating in a synchronization phase prior to steady state, wherein the synchronization phase comprises migrating the contents of the source disk to the destination disk.

12. The non-transitory computer readable storage medium of claim 11, further comprising entering the synchronization phase in response to at least one of receiving a request from the virtual machine manager or detecting an error in the replication of the set of write requests to the destination disk.

13. The non-transitory computer readable storage medium of claim 11, wherein the source disk is divided into a base image and an overlay image and only contents of the overlay image are migrated to the destination disk during the synchronization phase.

14. The non-transitory computer readable storage medium of claim 8, further comprising delaying processing of a write request to the source disk for a set period of time upon determining the contents stored on the source disk and the destination disk are equal.

15. A system comprising:

a memory;

a processing device, coupled to the memory, the processing device to perform operations comprising;

identifying, by the virtual machine monitor, a steady state wherein contents associated with a virtual machine stored on a source disk and a destination disk are equal;

receiving a set of write requests comprising data from a guest operating system of the virtual machine;

providing confirmation of a completion of the set of writes to the source disk;

asynchronously replicating the set of write requests to the destination disk;

receiving a flush request from the guest operating system of the virtual machine;

providing, to the guest operating system, confirmation of completion of a flush of the destination disk following replication of the set of write requests to the destination disk and writing of the data to persistent storage of the destination disk;

receiving a switch request from the virtual machine manager; and

switching the virtual machine to the destination disk and issuing subsequent write requests to the destination disk.

16. The system of claim 15, further comprising reporting to a virtual machine manager, by the virtual machine monitor, entry into the steady state.

17. The system of claim 15, wherein identifying the steady state further comprises:

maintaining a dirty bitmap to record one or more disk sectors that have been written to on the source disk but not the destination disk; and

emptying the dirty bitmap.

18. The system of claim 15, further comprising operating in a synchronization phase prior to steady state, wherein the synchronization phase comprises migrating the contents of the source disk to the destination disk.

19. The system of claim 18, further comprising entering the synchronization phase in response to at least one of receiving a request from the virtual machine manager or detecting an error in the replication of the set of write requests to the destination disk.

20. The system of claim 18, wherein the source disk is divided into a base image and an overlay image and only contents of the overlay image are migrated to the destination disk during the synchronization phase.