>From what you are saying, i think the problem may be the hardware, 
switches, or somthing hapening at the time the bad block are occuring.
I would do.
1. Check if the bad block errors are during a perticuler client backup.
2. Check errors on switches\server to pinpoint origin\backups etc.
3. IF you have the  option to change FC switch then do so.
4. If scsi then double check loose cables,card options set & error log, if 
posible to isolate the offending bus\card etc.
5. Open tickets with HBA vendors.
I dont belive the software is at fault ( Legato), you have to narrow down 
your choices as much as possible to get to the root cause.

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