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Date:      Tue, 16 Jul 2002 08:49:02 -0700
From:      Nick Sayer <nsayer@quack.kfu.com>
To:        Elliot Finley <efinleywork@efinley.com>
Cc:        freebsd-stable@freebsd.org
Subject:   Re: Poor Mans Software raid 1 on root partition?
Message-ID:  <3D34406E.3000502@quack.kfu.com>
References:  <20020715225138.V82789-100000@mail.allcaps.org> <011c01c22c8e$8e6d6f70$0900a8c0@P1200n> <00a001c22cd6$694888e0$035ad70a@PriceDMSDoc>

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Elliot Finley wrote:
> Here is what I do to make a bootable backup of my running system.

[...]


> /sbin/dump -0f - /usr | /sbin/restore -rf -

This is a... (I hesitate to use the word "bad", since it's not nearly 
bad as using dd) not-so-good thing to do with a live filesystem. What 
happens is that between phase 2 and 3 of the dump, the restore runs 
through the entire filesystem and makes all the directories. This is a 
*substantial* delay. In the meantime, the original filesystem can be 
changing. Level 0 backups need to be done when the filesystem is 
quiescent as possible anyway. Piping it to restore just makes things worse.

The better way is

dump | gxip > temporary_file
gzcat temporary_file | restore
rm temporary_file

One trick is to actually newfs your swap partition and use that for the 
temporary file, presuming your swap area is large enough to do the trick.

I do dump | restore all the time when I want to move from one disk to 
another, but I only do it in single-user mode. :-)


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