[BUG] Cannot restore ES 6.x index into OpenSearch2.x but the migration doc says it should work

[xiaoyuan0821]

Describe the bug

This migration doc https://opensearch.org/docs/2.11/upgrade-to/snapshot-migrate/ says we can restore Elasticsearch OSS 6.x indexes into OpenSearch 2.x, actually this doesn't work.

Related component

Other

To Reproduce

1. Take a snapshot of ES 6.x version
2. Try to restore to OpenSearch 2.11.1 cluster

POST /_snapshot/my_backup/snapshot_1/_restore
{
  "indices": "data*",
  "ignore_unavailable": true,
  "include_global_state": false,
  "rename_pattern": "(.+)",
  "rename_replacement": "$1"
}

4. See error

{
  "error": {
    "root_cause": [
      {
        "type": "snapshot_restore_exception",
        "reason": "[my_backup:snapshot_1/gvvMqKRXRk-C1BjLIjGLoQ] cannot restore index [data3] because it cannot be upgraded"
      }
    ],
    "type": "snapshot_restore_exception",
    "reason": "[my_backup:snapshot_1/gvvMqKRXRk-C1BjLIjGLoQ] cannot restore index [data3] because it cannot be upgraded",
    "caused_by": {
      "type": "illegal_state_exception",
      "reason": "The index [[data3/HYh8yLTQTwygtBVus4Wvjg]] was created with version [6.5.4] but the minimum compatible version is OpenSearch 1.0.0 (or Elasticsearch 7.0.0). It should be re-indexed in OpenSearch 1.x (or Elasticsearch 7.x) before upgrading to 2.11.0."
    }
  },
  "status": 500
}

Expected behavior

Should restore success

Additional Details

Plugins
Default plugins

[ticheng-aws]

Hi @xiaoyuan0821, the problem with snapshot restore occurs due to the use of a different Lucene version in your ES 6.x, which is not compatible with OpenSearch 2.x. One action item we can take here is to enhance the document's specificity regarding version compatibility for snapshot restore.