05/14/80	mrds.recovery

Function:	 This is a description of the procedure for backing up mrds databases
and then recovering to that earlier state of the database.


Procedure:  To obtain the backup copy of the database, do a quiesce_mrds_db on
the current database, then do a copy_dir of the database directory into another
part of the storage hierarchy, and finally do quiesce_mrds_db with the -free
option on the original database.


To return to the earlier state of the database that has been backed up, do a
quiesce_mrds_db of the current database, delete that database with a
delete_dir, do a copy_dir of the backup copy into the original storage
location, then finally do a quiesce_mrds_db with the -free option on the new
current database.


Notes:  The quiescing process is the only process that can open or update the
backup copy of the database.

The backup copy can be freed from the quiescent state if it is to be used for
program development, rather than a static backup copy.

A database quiesced by a dead process needs both a quiesce_mrds_db path -free,
an adjust_mrds_db path -trouble_switch off done to it.  However, there is
danger of an inconsistent database.

If display_mrds_db_status shows many open users, a long wait time may be needed
for quiesce_mrds_db.  However, a short wait time will work as a go/no_go test.
Also, dmdbs will show if the database is in a quiescent state.


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Historical Background

This edition of the Multics software materials and documentation is provided and donated
to Massachusetts Institute of Technology by Group BULL including BULL HN Information Systems Inc. 
as a contribution to computer science knowledge.  
This donation is made also to give evidence of the common contributions of Massachusetts Institute of Technology,
Bell Laboratories, General Electric, Honeywell Information Systems Inc., Honeywell BULL Inc., Groupe BULL
and BULL HN Information Systems Inc. to the development of this operating system. 
Multics development was initiated by Massachusetts Institute of Technology Project MAC (1963-1970),
renamed the MIT Laboratory for Computer Science and Artificial Intelligence in the mid 1970s, under the leadership
of Professor Fernando Jose Corbato. Users consider that Multics provided the best software architecture 
for managing computer hardware properly and for executing programs. Many subsequent operating systems 
incorporated Multics principles.
Multics was distributed in 1975 to 2000 by Group Bull in Europe , and in the U.S. by Bull HN Information Systems Inc., 
as successor in interest by change in name only to Honeywell Bull Inc. and Honeywell Information Systems Inc. .

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Permission to use, copy, modify, and distribute these programs and their documentation for any purpose and without
fee is hereby granted,provided that the below copyright notice and historical background appear in all copies
and that both the copyright notice and historical background and this permission notice appear in supporting
documentation, and that the names of MIT, HIS, BULL or BULL HN not be used in advertising or publicity pertaining
to distribution of the programs without specific prior written permission.
    Copyright 1972 by Massachusetts Institute of Technology and Honeywell Information Systems Inc.
    Copyright 2006 by BULL HN Information Systems Inc.
    Copyright 2006 by Bull SAS
    All Rights Reserved