From: esquel@sommarskog.se   
      
   Anton Shepelev (anton.txt@g{oogle}mail.com) writes:   
   > I am working on an in-house backup solution for our MSSQL   
   > databases, and have found that a differential backup may   
   > take considerable space (around 1 Mb)   
      
   I'm tempted to say that 1MB in size for a database back is very small.   
      
   > I want to make sure that my differential backups are not   
   > useless.  One solution is to compare byte-for-byte each new   
   > diff. backup with the previous one, and delete the copy if   
   > it turn out redundant, but I wondered if there were a   
   > simpler method.   
      
   To restore a database you need most recent full and most recent diff,   
   so keeping both is not really necessary. Unless you would want to   
   perform some sort of point-in-time restore. But normally, you use   
   log backups for that, not diff backups.   
      
   In any case, RESTORE HEADERONLY on the backup and checking last LSN   
   seems to be like a tenable solution. You could also use sys.fn_dblog   
   to find the last LSN - but keep in mind that this is an undocumented   
   and unsupported function.   
      
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