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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 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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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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