VastOne has written the best tutorial for fsarchive available on interweb,http://vsido.org/index.php?topic=217.0
About only thing VastOne can add there to improve is,
2: Run the savefs portion of fsarchiver.
single-dual core PC with 1GB or less RAM,
sudo fsarchiver -z7 savefs /mnt/iso/buildos.fsa /dev/sdc2
single-dual core PC with more than 1GB of RAM,
sudo fsarchiver -z8 savefs /mnt/iso/buildos.fsa /dev/sdc2
quod core PC with 4GB or less RAM,
sudo fsarchiver -j3 -z8 savefs /mnt/iso/buildos.fsa /dev/sdc2
quod core PC with more than 4GB of RAM,
sudo fsarchiver -j3 -z9 savefs /mnt/iso/buildos.fsa /dev/sdc2
PC with more than four cores and a plenty of RAM,
sudo fsarchiver -j4 -z9 savefs /mnt/iso/buildos.fsa /dev/sdc2
The above ensures performance-compression ratio is balanced.