dpx wrote:OB2LIMITBLKSIZE=0 - i couldn't find in .omnirc file this parameter but i can add and try.
You absolutely have to. For historic reasons (more related to shortcomings of HPUX and Solaris than Linux) the Unix MA refuses to use block sizes >256KiB by default, and this exact tunable will override that nonsense.
BTW, you don't have to reformat any tapes, that will happen automatically. The first time you write at the new (larger) block size, appending to not-yet-full tapes written at the old BS will fail with a warning, the tape will be ejected and DP continues on the next expired/unprotected/blank medium from the pool as it always does. And given it has to relabel that tape anyway, it uses the opportunity to relabel it at the new block size. All you see is a warning that this happened, so you can keep track of the progress. The new tape is then marked with a better write order number as well, so it will be used for writing from now on instead of the inappendable ones. The latter will bubble up in protection until they expire, and finally will be relabeled to the new BS as well when their time comes to be overwritten. The entire migration happens without any need to manually interfer - at least it did in countless migrations I performed from 64KiB to 256KiB and later 256KiB to 512KiB, on real tape and VTLs alike.
HTH,
Andre.