deal with several backup dirs.

backup

@@ -4,6 +4,7 @@ use strict;
 use Simba::CA;
 use POSIX qw(strftime);
 use Getopt::Long;
+use Filesys::Statvfs;
 
 my @filesets;
 
@@ -23,4 +24,18 @@ my $ca = Simba::CA->new({
 			});
 $ca->log_level(9);
 
+# find the backup dir with the most free space available.
+# other strategies are possible, like round robin, or daily, weekly,
+# etc. backups.
+
+my @backup_dirs = map {
+			$_ = $1 if m{(.*)/.*}; # basedir and detaint
+			my($bsize, $frsize, $blocks, $bfree, $bavail,
+			   $files, $ffree, $favail, $flag, $namemax)
+			    = statvfs($_);
+			[ $_, $bsize * $bavail ]
+                      } glob("/backup/*/active");
+@backup_dirs = sort { $b->[1] <=> $b->[0] } @backup_dirs;
+$ca->basedir($backup_dirs[0][0]);
+
 $ca->run();