Block Size for Tape with Legato system???

[Sylvie Vezina]

Hi, We are installing Legato system backup on HP -UX 11.00 and we've read this:
Important: The block size mode for tape devices used with the NetWorker software must be set to variable; otherwise, data recovery may fail. The block size mode for a tape device is set through the operating system. The procedure differs depending on the operating system. For information about setting the tape device block size mode, refer to the operating systemâ s documentation.

Could you help me, cause I don't have any ideas about that..
Than