the detailed log is:

    INFO: Starting new backup job - vzdump --compress --dumpdir /backup --tmpdir /data --suspend 101
    INFO: Starting Backup of VM 101 (openvz)
    INFO: status = CTID 101 exist mounted running
    INFO: starting first sync /vz/private/101 to /data/vzdumptmp699807
    INFO: Number of files: 305527
    INFO: Number of files transferred: 260118
    INFO: Total file size: 16218773322 bytes
    INFO: Total transferred file size: 15899992735 bytes
    INFO: Literal data: 15899995944 bytes
    INFO: Matched data: 0 bytes
    INFO: File list size: 6898650
    INFO: File list generation time: 0.001 seconds
    INFO: File list transfer time: 0.000 seconds
    INFO: Total bytes sent: 15920366346
    INFO: Total bytes received: 5458387
    INFO: sent 15920366346 bytes  received 5458387 bytes  9278080.24 bytes/sec
    INFO: total size is 16218773322  speedup is 1.02
    INFO: first sync finished (1717 seconds)
    INFO: suspend vps
    INFO: Setting up checkpoint...
    INFO: Error: No checkpointing support, unable to open /proc/cpt: No such file or directory
    ERROR: Backup of VM 101 failed - command '/usr/sbin/vzctl chkpnt 101 --suspend' failed with exit code 16