DUMP(V)                      2/11/75                      DUMP(V)


     dump - incremental dump tape format


     The dump and restor commands are  used  to  write  and  read

     incremental dump magnetic tapes.

     The dump tape consists of blocks  of  512-bytes  each.   The

     first block has the following structure.

     struct {

             int     isize;

             int     fsize;

             int     date[2];

             int     ddate[2];

             int     tsize;


     Isize, and fsize are the corresponding values from the super

     block  of  the  dumped  file system.  (See file system (V).)

     Date is the date of the dump.  Ddate is the incremental dump

     date.   The  incremental  dump  contains  all files modified

     between ddate and date.  Tsize is the number of  blocks  per

     reel.  This block checksums to the octal value 031415.

     Next there are enough whole tape blocks to contain one  word

     per  file  of the dumped file system.  This is isize divided

     by 16 rounded to the next higher integer.   The  first  word

     corresponds  to  i-node  1,  the  second to i-node 2, and so

     forth.  If a word  is  zero,  then  the  corresponding  file

     exists,  but was not dumped.  (Was not modified after ddate)

     If the word is -1, the file does not  exist.   Other  values

     for the word indicate that the file was dumped and the value

     is one more than the number of blocks it contains.

     The rest of the tape contains for each dumped file a  header

     block  and  the  data  blocks  from  the  file.   The header

     contains an exact copy of the i-node (see file  system  (V))

     and  also checksums to 031415.  The next-to-last word of the

     block  contains  the  tape   block   number,   to   aid   in

     (unimplemented)  recovery  after tape errors.  The number of

     data blocks per file is directly specified  by  the  control

     word  for  the  file and indirectly specified by the size in

     the i-node.  If these numbers differ, the  file  was  dumped

     with a `phase error'.


     dump (VIII), restor (VIII), file system(V)