Kern, thanks for your reply. 
My SD running on RHEL 6.
Yes, my spool file located at NAS mount, but it's very fast and stable storage.


I've changed following options:
BSF at EOM = No
TWO EOF = No
Now it works fine.

My config file:

Device {
  Name = "LTO6-Drive-1"
  Device Type = tape
  Media Type = LTO-6
  Drive Index = 0;
  Archive Device = /dev/tape5
  Hardware End of Medium = yes
  BSF at EOM = No
  Use MTIOCGET = yes;
  RandomAccess = no;
  Block Checksum = yes;
  TWO EOF = No
  Backward Space Record = yes;
  Forward Space Record = yes;
  Fast Forward Space File = Yes
  Block Positioning = yes;
  AutomaticMount = yes; # when device opened, read it
  AlwaysOpen = yes;
  RemovableMedia = yes;
  Autochanger = yes;
  LabelMedia = yes;
  Alert Command = "sh -c 'smartctl -d scsi -H -l error %c'"
  Spool Directory = /mnt/bacula/td5
  Maximum Volume Size = 2450 GB
  Autoselect = yes
  }

Works fine. Thanks for attention, problem solved.

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