Without snapshots there is some risk to get inconsistent set of files when you make a backup of live file system. In general this is a problem but I'm not sure about your case. Actually there is another solution to this problem shutdown the system and take the backup using bootable CD/DVD (or booting from another OS installation).

You should unmount a file system before backing up with dd. You can also take a look at Clonezilla which is an open-source image-backup software.

2009/6/21 Rafał Radecki <radecki.rafal@gmail.com>
I think about using dd instead of dump? Is this an acceptable idea?

2009/6/21 Robert Heller <heller@deepsoft.com>

At Sun, 21 Jun 2009 11:49:09 +0200 CentOS mailing list <centos@centos.org> wrote:

>
>
>
> Hi all. I'm currently having a following problem: I have only ssh connection
> to a CentOS 5.2 system, there are two harddiscs on it. One stores the system
> (/ filesystem) and the other should be used to help restore the system in
> case of first disks' failure. I thought that maybe dump would be a good
> utility to make it. But in only works on read-only filesystems. In one

Dump works just fine on a read-write file system.  There is the pretty
much standard limitation (that applies to *all* backup methods) that
when backing up an 'active' file system: there will always be files that
will miss the backup because they were being written during the backup
process.

> article I've read that making a snapshot of the / filesystem (then it
> wouldbe read-only) and backing it could help. But aren't snapshots limited
> to logical volumes (LVM)?  My friend told me to use rsync to back up the
> entire / filesystem to the second disk and then in case o failure the system
> from the copy should boot ok.
>
> Could anyone provide any suggestions? I don't have physical contact with the
> machine so for example RAID 1 isn't a possible option/
>
> Any help will be very kindly appreciated.

Make an initial dump to get the base system copied, then set up a cron
job to sync the disks once a day (or more frequently) with rsync.

>
> With regards,
> R.
>
> MIME-Version: 1.0
>
> _______________________________________________
> CentOS mailing list
> CentOS@centos.org
> http://lists.centos.org/mailman/listinfo/centos
>
>

--
Robert Heller             -- 978-544-6933
Deepwoods Software        -- Download the Model Railroad System
http://www.deepsoft.com/  -- Binaries for Linux and MS-Windows
heller@deepsoft.com       -- http://www.deepsoft.com/ModelRailroadSystem/

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