diff --git a/Notes b/Notes
index 45ff579..47a90d7 100644
--- a/Notes
+++ b/Notes
@@ -63,11 +63,7 @@ Tape performance:
 
 Equality checking doesn't work for setuid files.
 
-Implement equality checking via saved checksum.
-
-checksum is null if file is linked. Is that ok? Can this be solved
-together with the previous point?
-
 exit if disk full
 
-Move prune list to config file.
+On my 800 MHz PIII, the CPU usage is rather high. Some profiling seems
+to be necessary (or I should get a faster backup server :-)).
diff --git a/lib/Simba/CA.pm b/lib/Simba/CA.pm
index 57f6778..123e218 100644
--- a/lib/Simba/CA.pm
+++ b/lib/Simba/CA.pm
@@ -156,8 +156,15 @@ sub backup2disk {
                     } else {
                         $self->log(5, "unexpected trailer $trailer\n");
                     }
-                    $self->setmeta($f);
-                    $self->log(10, "stored");
+                    my $oldfile = $self->finddup($f);
+                    if ($oldfile) {
+                        unlink($backup_filename) or die "cannot unlink $backup_filename: $!";
+                        link($oldfile, $backup_filename) or die "cannot link $oldfile to $backup_filename: $!";
+                        $self->log(10, "linked (dup)");
+                    } else {
+                        $self->setmeta($f);
+                        $self->log(10, "stored");
+                    }
                 } else {
                     $self->log(5, "unexpected header $header\n");
                 }
@@ -421,6 +428,7 @@ sub close_session {
 
 sub get_last_session_id {
     my ($self) = @_;
+    return unless $self->{last_backup};
     my $sessions = $self->{dbh}->selectall_arrayref("select * from sessions where prefix=?",
                                                     { Slice => {} },
                                                     $self->{last_backup});
@@ -428,5 +436,49 @@ sub get_last_session_id {
     return $sessions->[0]{id};
 }
 
+=head2 finddup
+
+Find a duplicate of the current file in the database. This is useful if you
+have multiple copies of a file stored in different locations.
+
+=cut
+
+sub finddup {
+    my ($self, $f) = @_;
+    my $sth = $self->{dbh}->prepare("select * from versions, files, sessions 
+                                     where file_type=? and file_size=? and file_mtime=?
+                                       and file_owner=? and file_group=? and file_acl=?
+                                       and file_unix_bits=? 
+                                       and checksum=? and online=1
+                                       and versions.file=files.id and versions.session=sessions.id");
+    $sth->execute(
+             $f->{t}, $f->{s}, $f->{m},
+             $f->{o}, $f->{g}, $f->{acl},
+             join(',', map {$f->{$_} ? ($_) : ()} qw(setuid setgid sticky)),
+             $f->{checksum}
+          );
+    while (my $r = $sth->fetchrow_hashref()) {
+        my $oldfile = "$r->{prefix}/$r->{path}";
+        if (my $st = lstat($oldfile)) {
+            if ($st->mtime          == $f->{m} &&
+                $st->size           == $f->{s} &&
+                $st->uid            == $self->name2uid($f->{o}) &&
+                $st->gid            == $self->name2gid($f->{g}) &&
+                ($st->mode & 07777) == $self->acl2mode($f)
+            ) {
+                $sth->finish();
+                return $oldfile;
+            }
+        }
+    }
+    return;
+}
+
+sub DESTROY {
+    my ($self) = @_;
+    $self->{dbh}->disconnect();
+}
+
+
 # vim: tw=0 expandtab
 1;
diff --git a/t/01_ca.t b/t/01_ca.t
index c1fa9fe..c755478 100644
--- a/t/01_ca.t
+++ b/t/01_ca.t
@@ -6,7 +6,8 @@ use Test::More tests => 15;
 
 BEGIN { use_ok( 'Simba::CA' ); }
 
-my $ca = Simba::CA->new({ dbi_file => $ENV{SIMBA_DB_CONN} || "$ENV{HOME}/.dbi/simba"});
+my $ca = Simba::CA->new({ dbi_file => $ENV{SIMBA_DB_CONN} ||
+				      "$ENV{HOME}/.dbi/simba_test"});
 ok($ca, 'new CA');
 
 my $uid;
diff --git a/t/02_ca.t b/t/02_ca.t
new file mode 100644
index 0000000..082faf2
--- /dev/null
+++ b/t/02_ca.t
@@ -0,0 +1,61 @@
+#!/usr/bin/perl
+use warnings;
+use strict;
+
+# Live tests.
+#
+# These tests need to be run as simba_ca and it needs to be able to
+# connect to simba_da@localhost.
+
+use Test::More tests => 8;
+
+use File::stat;
+
+BEGIN { use_ok( 'Simba::CA' ); }
+
+my $ca = Simba::CA->new({ dbi_file => $ENV{SIMBA_DB_CONN} ||
+				      "$ENV{HOME}/.dbi/simba_test"});
+
+ok($ca, 'new CA');
+
+# make sure filesets contains test data then connect again:
+$ca->{dbh}->do("delete from filesets");
+$ca->{dbh}->do("insert into filesets(host, dir) values('localhost', '/var/tmp/simba_test')");
+
+$ca = Simba::CA->new({ dbi_file => $ENV{SIMBA_DB_CONN} ||
+				   "$ENV{HOME}/.dbi/simba_test"});
+
+ok($ca, 'new CA 2');
+
+
+SKIP: {
+    skip "not running as root", 1 unless $> == 0;
+    mkdir "/var/tmp/simba_test";
+    mkdir "/var/tmp/simba_test/d1";
+    mkdir "/var/tmp/simba_test/d2";
+
+    open my $fh, '>:raw', '/var/tmp/simba_test/d1/f1';
+    print $fh "test\n";
+    close($fh);
+
+    open $fh, '>:raw', '/var/tmp/simba_test/d2/f2';
+    print $fh "test\n";
+    close($fh);
+
+    $ca->run();
+    my $this_backup = $ca->{this_backup};
+    my $st1 = lstat("$this_backup/d1/f1");
+    ok($st1, "file 1 exists");
+    is($st1->nlink, 2, "file 1 has 2 links");
+    my $st2 = lstat("$this_backup/d2/f2");
+    ok($st2, "file 2 exists");
+    is($st2->nlink, 2, "file 2 has 2 links");
+    is($st1->ino, $st2->ino, , "file 1 and 2 are the same");
+
+    # cleanup
+    system("rm", "-rf", $this_backup);
+    $ca->{dbh}->do("delete from versions");
+    $ca->{dbh}->do("delete from files");
+    $ca->{dbh}->do("delete from filesets");
+
+}