Backup root partition with dd without downtime

You can use the free Idera R1Soft Hot Copy utility to accomplish this.

This is a utility that installs as a kernel module and allow you to take a copy-on-write snapshot of a running system. You can install it and run on-the-fly without a reboot.

The result is that you can create an on-demand read-write or read-only snapshot of any of your mounted filesystems. They'll show up in a path similar to /var/hotcopy/[device_name]_hcp1/ by default, but the mountpoint is also configurable... (I use /backup)

I actually use Hot Copy to augment the regular tape backups on my standalone Linux servers. It removes file-contention issues and gives a more accurate backup.

When done, you destroy the snapshot and continue as normal.

This component is a the core of the commercial R1Soft CDP backup software suite, but is an extremely handy way to obtain Linux system snapshots without LVM, ZFS or Btrfs.