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The Castor-System-Delete-Marker-Etag header (e.g., Castor-System-Delete-Marker-Etag: " b529363121092e11da6dc1964faf1923") is returned on a DELETE operation on a named or alias object that is either in the versioning enabled or versioning suspended state for the object. If versioning is disabled, the object is immutable or a context, and no such header is returned. Check the ETag of the delete marker (returned) by INFO-ing the deleted object and checking the returned ETag header.
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