This is a customized version of [this script](http://pastie.org/199267):
```ruby
require 'find'
namespace :db do
desc "Backup the database to a file. Options: DIR=base_dir RAILS_ENV=production MAX=20"
task :backup => [:environment] do
datestamp = Time.now.strftime("%Y-%m-%d_%H-%M-%S")
base_path = ENV["DIR"] || "db"
backup_base = File.join(base_path, 'backup')
backup_folder = File.join(backup_base, datestamp)
backup_file = File.join(backup_folder, "#{RAILS_ENV}_dump.sql.gz")
FileUtils.mkdir_p(backup_folder)
db_config = ActiveRecord::Base.configurations[RAILS_ENV]
pass = ''
pass = '-p' + db_config['password'] if db_config['password']
cmd = "mysqldump -P #{db_config['port']} -h #{db_config['host']} -u #{db_config['username']} #{pass} #{db_config['da
tabase']} -Q --add-drop-table -O add-locks=FALSE -O lock-tables=FALSE | gzip -c > #{backup_file}"
sh cmd
dir = Dir.new(backup_base)
all_backups = dir.entries[2..-1].sort.reverse
puts "Created backup: #{backup_file}"
max_backups = (ENV["MAX"] || 20).to_i
puts max_backups
unwanted_backups = all_backups[max_backups..-1] || []
for unwanted_backup in unwanted_backups
FileUtils.rm_rf(File.join(backup_base, unwanted_backup))
puts "deleted #{unwanted_backup}"
end
puts "Deleted #{unwanted_backups.length} backups, #{all_backups.length - unwanted_backups.length} backups available"
end
end
```