Corrupt image copy questions

 We normally backup our active datafiles nightly with a script-generated command like :

run {

        allocate channel d1 type disk;

        copy

                datafile '$1'

                to '$2'

                level 0

                check logical;

}

 

These backups are pointed to a SAN location.  On three occasions recently I have attempted an rman duplicate db only to have a failure caused by a corrupt backup.

I immediately run dbv on the production file and find no problem.  In the alert log I find only 

Hex dump of (file 152, block 1) in trace file /u01/oracle/diag<<stuff del>>/trace/XXXX_ora_20103.trc

Corrupt block relative dba: 0x26000001 (file 152, block 1)