> I wonder that BackupPC knows how often a host was reachable or not but I
> can't find a file where this information is stored.
The host status is stored the BackupPC server. It is periodically
saved to the $TOPDIR/log/status.pl file so that it can be restored
if you restart BackupPC.
You can get the values for all hosts with:
BackupPC_serverMesg status hosts
or a specific host with:
BackupPC_serverMesg 'status host(HOSTNAME)'