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• Introduction
  • Purpose
  • References
  • Document History
  • Glossary
• Feature Specifications
  • Use cases
• Architecture and Design description
  • web services APIs
• UI flow
• Appendix
  • Appendix A:
  • Appendix B:

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Features that need to be supported
- Create/delete data volume on local storage
- Attach/detach data volume on local storage
- Disk offering leveraging local storage
- Number of local data volumes that can be attached (capped by some number or no limit?). Currently there is a fixed limit (13 for XS 6.0 and above, 6 for other HVs) on the number of volumes that can be attached to a VM 

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Root and data disk combinations
- Local root + Local data. This is the primary scenario that needs to be enabled
- Shared root + Local data. This combination will not be blocked explicitly but I cannot think of any use case for this
- Local root + Shared data. This is already supported
- Shared root + Shared data. This is already supported 

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Zone level config for enabling local storage
- Currently local storage offering is at the cloud level. The idea is to have a zone level setting for enabling local storage offering for both compute and disk. If local storage is not enabled then VMs cannot be created using compute/disk offering leveraging local storage in that zone.

Hypervisor support
- For now only XenServer, going forward support for remaining ones will be added. Note that there is no explicit check to prevent creation of local volumes on the remaining hypervisors., Vmware, KVM.

Architecture and Design description

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ALTER TABLE `cloud`.`data_center` ADD COLUMN `is_local_storage_enabled` tinyint NOT NULL DEFAULT 0 COMMENT 'Is local storage offering enabled for this data center; 1: enabled, 0: not';
UPDATE `cloud`.`data_center` SET `is_local_storage_enabled` = IF ((SELECT `value` FROM `cloud`.`configuration` WHERE `name`='use.local.storage')='true', 1, 0) WHERE `removed` IS NULL;

Allocator changes

FirstFit storage Local storage pool allocator is modified to take into account only local storage pools from host where vm instance is placed while allocating a local data volume. Allocation logic for shared volumes remains unchanged.

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Hack for creating data disk (in existing code)
- Create a VM with local ROOT disk
- Take a snapshot of this
- Create a volume from the snapshot, this is created on the local storage

Appendix B:

Questions
- What happens when a VM with local data disk is deleted? Should the data disk gets cleaned up? In ec2 gets cleaned up. In CS for shared data disk it gets detached
- Detach/attach of local disk. Once attached to an instance should we allow re-attach to another VM instance (ec2 doesn't)?