I was trying to backup my Zimbra mail server and since i have no previous experiment, i wanted to archive all data for less space on storage -the disk usage was at 88%- then i typed the command

tar -cvf /dev/sdb /opt/zimbra

and it started normally, but after a while i noticed that the communication between me and the server is not working

then i tried to cancel it by ctl+Z the job stopped but the server went down totally
and when it reboots

it shows me a prompt (initramfs)

can any body help on this?

what to do, and what happend?