Snapshot access using nocopy undefined thin devices
A thin device (TDev) is tagged to identify the TDev as being used to access snapshot data on the storage system. If a snapshot is to be shipped to a cloud repository, the tagged TDev is linked to the snapshot, and mounted to a cloud tethering subsystem. When the tagged TDev is linked to the cloud tethering subsystem, the snapshot subsystem reads the thin device tag and, if the thin device is tagged, selectively does not execute a define process on the tagged thin device. By not executing the define process, the tracks of the thin device do not contain metadata identifying the location of the snapshot data on the storage system. Writes to source do not require a private copy of the old data for the snapshot, even if the snapshot is created in a different storage resource pool than the source data volume.
1. A non-transitory tangible computer readable storage medium having stored thereon a computer program for providing snapshot access using a nocopy undefined thin device, the computer program including a set of instructions which, when executed by a computer, cause the computer to perform a method comprising the steps of:
creating a snapshot of a production volume by a snapshot subsystem;
linking the snapshot to a thin device;
inspecting, by the snapshot subsystem, the thin device for the presence of a tag identifying the thin device as being used by a cloud tethering subsystem in connection of movement of the snapshot to a cloud repository;
when the tag doesn't exist on the thin device:
implementing a define process on the thin device by the snapshot subsystem, the define process changing pointers of tracks of the thin device to identify locations of backend data of the snapshot of the production volume;
mounting the untagged thin device in a host application;
issuing data read operations, by the host application, on the tracks of the untagged thin device; and
when the tag exists on the thin device:
not implementing the define process on the tagged thin device by the snapshot subsystem;
mounting the tagged thin device in the cloud tethering subsystem; and
issuing data read operations, by the cloud tethering subsystem, on the tracks of the tagged thin device.
2. The non-transitory tangible computer readable storage medium of claim 1 , wherein the production volume has data stored on backend allocations of tracks of memory, and wherein not implementing the define process on the tagged thin device causes the tagged thin device to remain undefined such that tracks of the tagged thin device do not contain pointers to the backend allocations of the tracks of memory of the production volume.
3. The non-transitory tangible computer readable storage medium of claim 2 , further comprising the step of executing the issued data read operations by a front-end adapter of a storage system, and wherein the step of executing the data read operations, by the front end adapter, comprises issuing a respective request, for each data read operation, to a data services subsystem to resolve the data address associated with the respective data read operation.
4. The non-transitory tangible computer readable storage medium of claim 3 , further comprising sending, by the data services subsystem, a request to a snapshot subsystem for a one time on-demand determination of a location of a requested track of the thin device associated with the respective read operation.
5. The non-transitory tangible computer readable storage medium of claim 4 , further comprising receiving, by the data services subsystem, a response from the snapshot subsystem, with a data track number where the requested data resides on the storage system.
6. The non-transitory tangible computer readable storage medium of claim 5 , further comprising not storing the data track number in the tagged thin device, such that the track of the tagged thin device remains undefined even after execution of the read operation on the track of the tagged thin device.
7. The non-transitory tangible computer readable storage medium of claim 5 , further comprising allocating a slot in a shared global memory, by the data services subsystem, and copying the requested data from the data track where the requested data resides on the storage system to the allocated slot in the shared global memory.
8. The non-transitory tangible computer readable storage medium of claim 7 , further comprising forwarding, by the front-end adapter, the requested data from the allocated slot in the shared global memory to the cloud repository.
9. A method of providing snapshot access using a nocopy undefined thin device, the method comprising the steps of:
creating a snapshot of a production volume by a snapshot subsystem;
linking the snapshot to a thin device;
inspecting, by the snapshot subsystem, the thin device for the presence of a tag identifying the thin device as being used by a cloud tethering subsystem in connection of movement of the snapshot to a cloud repository;
when the tag doesn't exist on the thin device:
implementing a define process on the thin device by the snapshot subsystem, the define process changing pointers of tracks of the thin device to identify locations of backend data of the snapshot of the production volume;
mounting the untagged thin device in a host application;
issuing data read operations, by the host application, on the tracks of the untagged thin device; and
when the tag exists on the thin device:
not implementing the define process on the tagged thin device by the snapshot subsystem;
mounting the tagged thin device in the cloud tethering subsystem; and
issuing data read operations, by the cloud tethering subsystem, on the tracks of the tagged thin device.
10. The method of claim 9 , wherein the production volume has data stored on backend allocations of tracks of memory, and wherein not implementing the define process on the tagged thin device causes the tagged thin device to remain undefined such that tracks of the tagged thin device do not contain pointers to the backend allocations of the tracks of memory of the production volume.
11. The method of claim 10 , further comprising the step of executing the issued data read operations by a front-end adapter of a storage system, and wherein the step of executing the data read operations, by the front end adapter, comprises issuing a respective request, for each data read operation, to a data services subsystem to resolve the data address associated with the respective data read operation.
12. The method of claim 11 , further comprising sending, by the data services subsystem, a request to a snapshot subsystem for a one time on-demand determination of a location of a requested track of the thin device associated with the respective read operation.
13. The method of claim 12 , further comprising receiving, by the data services subsystem, a response from the snapshot subsystem, with a data track number where the requested data resides on the storage system.
14. The method of claim 13 , further comprising not storing the data track number in the tagged thin device, such that the track of the tagged thin device remains undefined even after execution of the read operation on the track of the tagged thin device.
15. The method of claim 13 , further comprising allocating a slot in a shared global memory, by the data services subsystem, and copying the requested data from the data track where the requested data resides on the storage system to the allocated slot in the shared global memory.
16. The method of claim 15 , further comprising forwarding, by the front-end adapter, the requested data from the allocated slot in the shared global memory to the cloud repository.