lfs data_version (LL_IOC_DATA_VERSION) on an EC file with a data stripe on an unavailable OST blocks until the OST returns, so lfs mirror resync/verify, HSM archive and lfs migrate of an otherwise readable file hang. See the LU-20212 test results.

osc_io_data_version_end < cl_io_end < lov_io_end_wrapper < lov_io_data_version_end < cl_io_end < cl_io_loop < ll_ioc_data_version < ll_file_ioctl

66567 (LU-20212) only fails fast for a deactivated import. For a file in RDONLY state the objects cannot change while the layout lock is held, so the version could be taken without the unavailable object, or the RPC could at least be sent no-delay and fail with an error the tools can handle.