KB2243: Backup job fails with “The ... - Veeam Software
https://www.veeam.com/kb224310.02.2017 · A backup job targetted at an ReFS 3.0 based repository fails with “The request is not supported. Failed to duplicate extent" Examples: Agent: Failed to process method {Transform.CompileFIB}: The request is not supported. Failed to duplicate extent. Target file: <path>vbk, Source file: <path>vib, TgtOffset: xx, SrcOffset: yy, DataSize: 4096