[DOC] Subpage for Snapshot Interoperability with Remote Store

[harishbhakuni]

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We need to add a subpage for Shallow Copy Snapshots.

Shallow Copy Snapshots (or Snapshot Interoperability w/ Remote Store)

We now support Shallow copy snapshots as well for Remote Store Enabled Indices. The idea is, as the data is already stored in remote store repository, instead of storing the entire segment data again in snapshot repository we will be using a reference to that data in snapshot repository. User can enable shallow copy snapshots by enabling remote_store_index_shallow_copy repository setting for the snapshot repository. All the snapshot APIs will remain same for these snapshots as well.

Few points to note/consider for shallow copy snapshots:

• Shallow copy snapshots are supported only for Remote Store Enabled Indices.
• User should trigger shallow copy snapshots once all the nodes are on version >=2.10.
• Once this setting is enabled, we do not recommend disabling this setting from the repository.
• For these snapshots as the segment data will not be stored in snapshot repository, these will be faster than normal snapshots.
• We do not store any segment data in snapshot repository as part of these snapshots, so the file size diff for the shards of these snapshots will be zero.
• Searchable Snapshots would not be supported with Shallow Copy Snapshots.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.