my $dir = "/mnt/home/volume/";
my $i = 0;
while(1) {
    $i++;
    my $success = 1;
    sysopen (FH, $dir . "$i", O_RDWR|O_EXCL|O_CREAT) or $sucess = 0;
   last if $success;
}
# Now it should be safe to create dir $i