Back-up SATA rootfs without dismount the disk. (4 replies)

Hollo everyody.
I have read all the wiky for the back-up but I have not found a wicky for a Backup rootfs using tar command from SATA to USB without dismounting the HD (there is a similar one for cloning but I would prefer a tar file).

Before to make the wrong thing I would like to ask if this will work:

1) boot as normal with last u-boot from SATA rootfs
2) change rootfs LABEL to SATA_rootfs
3) power-off
3) insert a USB drive with preinstalled rootfs
4) switch on and boot from USB rootfs (sata should be disreguarded because of different label)
5) cd to SATA_rootfs disk
6) time tar -cjf /srv/nsa325/my-rootfs.tar.bz2 . &
7) re label SATA_rootfs --> rootfs
8) power-off
9) unplug USB rootfs
10) reboot as normal from SATA rootfs

The idea is to use USB rootfs boot to backup by SATA rootfs on the NAS hd mounted in /srv/nsa325

WIll this work ?

Thanks