Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!brl-adm!umd5!ames!oliveb!felix!zemon
From: tankus@hsi.UUCP (Ed Tankus)
Newsgroups: comp.unix.ultrix
Subject: Re: Dump/Restore help needed
Message-ID: <22150@felix.UUCP>
Date: 19 Feb 88 22:03:14 GMT
References: <20938@felix.UUCP>
Sender: zemon@felix.UUCP
Reply-To: tankus@hsi.UUCP (Ed Tankus)
Organization: Health Systems Intl., New Haven, CT
Lines: 77
Approved: zemon@felix.UUCP
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Art Zemon gives a very detailed view of this procedure.  However, such detail
may not always be necessary nor practical.

We have a lot of activity on 2 VAX's, consequently, many files are modified
and many new files are created.  We were faced with several problems.

	1) Maximize the number of files dumped 
	2) Minimize the number of tapes used (no more than one per file system)
	3) Provide plenty of redundancy in case a bad tape occurs.
	4) Make it fast and easy to restore files.

We have been using the following procedure with great success for about 2 years.


		M   Tu  W  Th  F 

        VAX #1	1   1   1  2   1
			   0   

	VAX #2  1   1   1  1   2
			       0

Monday thru Wednesday we perform a level 1 dump of our normal files systems.
The level 1 picks up all new or modified files since the last level 0, i.e.,
Thursday or Friday.  No more than half a 2400' mag tape at 6250 bpi is ever
used for a level 1. It's usally only about 25%, even by Wednesday.

Thursday morning our first VAX is brought to single user and a level 2 dump
performed on the normal filesystems.  This picks up everything new or modified
since the day before.  A level 0 dump is performed immediately after the
level 2 dumps are completed.  The same scenario applies to Friday for the
second VAX.

This scenario provides alot of redundancy and a large safety net for us. Using
this scheme, we could "theorhetically" lose the dump tapes (for VAX #2) for
Monday thru Wednesday and still be back to business as usual quickly. How?

Each level 1 refers back to the previous level 0.  Each level 2 refers back
to the previous level 1.

VAX #2
	0
	| <- 1 (Mon)
	| <- 1 (Tue)
	| <- 1 (Wed)
	| <- 1 (Thu)
	|    | <- 2 (Fri)
	|    .
	.
	0, etc.
	
As the picture shows, given a system crash anytime after the level 2 dump,
the only tapes that would be needed would be the previous level 0, the 
level 1 from Thusday, and the level 2 from Friday.  Even if the PREVIOUS
level 0 was bad, we simulate that tape be using a level 0 from TWO WEEKS
previous and the associated level 1's and 2 's.

Because of the size of our filesystems, we reuse our level 1's and 2's
starting every 4th week.  We rotate tape sets every week so that the 
two most recent set of level 0 dumps are always off-site.

This same scheme should work for TK50's, though this level of redundancy may
not be necessary for a MicroVAX.  This isn't foolproof either. Just another
way of doing things.

Sorry for the length but I thought the explanation might save others some time.


Cheers!

-- Ed.
    
Net  :  {uunet,ihnp4,noao,yale}!hsi!tankus
Snail:  Health Systems Int'l, 100 Broadway, New Haven, CT 06511
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