[CentOS] Backup live system

Thu Oct 20 18:07:37 UTC 2011
Brian Mathis <brian.mathis+centos at betteradmin.com>

On Thu, Oct 20, 2011 at 10:52 AM, ken <gebser at mousecar.com> wrote:
> Though I've worked with enterprise systems, I'm not familiar with FOOS
> backup software.  Which of those recommended would allow me to backup a
> system while users are active on it?  If it matters the system uses LVM.
>    I'd also like to be able to avoid needing the network if possible.
> That is, I'd plug in a disk into a USB port and backup the system onto
> that... again, while the system is live.
> Thanks much.

Others have said that file are not locked on Linux, so you can back
them up anyway, but this is surely not your point.

The only way to get a consistent backup is to create a snapshot and
back that up.  If this is a VM you should be able to make a snapshot
and then back up the VM files.  LVM is a good way to do it on both
physical and virtual machines, but there are a few caveats:

- You need free PEs on the volume group.  When you make an LVM
snapshot it needs this extra space to store the changed blocks while
the snapshot is in existence.  Most default LVM installs do not
reserve spare PEs for this.  The amount of free PEs you need is
completely dependent on how many changes get made to the volume while
the snapshot exists.  If you run out of PEs, the behavior is

- There is a huge performance penalty.  As long as any snapshot
exists, there is at least a 50% performance hit.  If this is a high
performance database server, you might not be able to afford it.  Make
sure to do your backup on slow times.

The howtoforge link seems to cover most of the mechanics.

-☙ Brian Mathis ❧-