Features/SnapshotsMultipleDevices/CommandSetProposals: Difference between revisions
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:Poses fewest problems in adding new kinds of operations. oVirt usecase falls out nicely. | :Poses fewest problems in adding new kinds of operations. oVirt usecase falls out nicely. Subsumes group snapshots too, but management would have to provide its own error handling. | ||
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:Requires changes to Jeff's patches. Management probably cannot provide the improvements in error handling provided by Jeff's patches. Core infrastructure changes needed for freeze/unfreeze. | :Requires changes to Jeff's patches. Management probably cannot provide the improvements in error handling provided by Jeff's patches. Core infrastructure changes needed for freeze/unfreeze. |
Revision as of 21:25, 27 February 2012
Two different patch series posted on the mailing list sparked a discussion on block device operations (snapshotting, enabling mirroring, switching to a different image) that have to be performed atomically.
This page documents the four approaches that were discussed.
Jeff Cody
{ 'type': 'SnapshotDev', 'data': {'device': 'str', 'snapshot-file': 'str', '*format': 'str' } } { 'command': 'blkdev-group-snapshot-sync', 'data': { 'devlist': [ 'SnapshotDev' ] } }
A single command prepares snapshots for many devices and commits the transaction if all snapshots are successfully prepared.
- Advantages
- Patches are almost ready for inclusion. Simple interface with only one command.
- Disadvantages
- No support for reopening and mirroring. Introducing them later is possible, but needs to be done before 1.1 in case API changes are needed.
- Improved error handling does not extend to the existing blockdev-snapshot-sync command.
Federico Simoncelli
{ 'drive-reopen', 'data': { 'device': 'str', 'source': 'str', '*format': 'str' } } { 'drive-migrate', 'data': { 'device': 'str', 'dest': 'str', '*dest-format': 'str', 'new-source': 'str', '*source-format': 'str' } }
- Advantages
- Patches on the mailing list.
- Disavantages
- Complicated interface tailored only on the oVirt usecase (Paolo tried to shoehorn other cases in the same drive-migrate command, but with little success). Doesn't extend to mirroring multiple devices.
Paolo Bonzini
{ 'command' : 'blockdev-start-transaction' } { 'command' : 'blockdev-commit-transaction' } { 'command' : 'blockdev-abort-transaction' } { 'command' : 'drive-reopen', 'data': { 'device': 'str', 'source': 'str', '*format': 'str' } } { 'command' : drive-mirror, 'data': { 'device': 'str', 'dest': 'str', '*format': 'str' } }
- Advantages
- Uniform handling of all cases. oVirt usecase falls out nicely. Improved error handling extends to the existing blockdev-snapshot-sync command.
- Disadvantages
- Requires changes to Jeff's patches. Core infrastructure changes needed for transactions (though most of the algorithms are already found in Jeff's patches).
The existing blockdev-snapshot-sync command would need changes to support invocations in a transaction.
Anthony Liguori
{ 'command' : 'blockdev-freeze', 'data': { 'device': 'str' } } { 'command' : 'blockdev-unfreeze', 'data': { 'device': 'str' } } { 'command' : 'drive-reopen', 'data': { 'device': 'str', 'source': 'str', '*format': 'str' } } { 'command' : drive-mirror, 'data': { 'device': 'str', 'dest': 'str', '*format': 'str' } }
- Advantages
- Poses fewest problems in adding new kinds of operations. oVirt usecase falls out nicely. Subsumes group snapshots too, but management would have to provide its own error handling.
- Disadvantages
- Requires changes to Jeff's patches. Management probably cannot provide the improvements in error handling provided by Jeff's patches. Core infrastructure changes needed for freeze/unfreeze.