Block Device Mapping

關於創建實例的時候添加各種磁盤以及其他設置的boto使用方法，下面給個例子
一般建議字母A用作根分區，B到E用做實例存儲（InstanceStore，ephemeral），F以後用作EBS, 只是個規範建議，非不這麼搞也行
基本是先用BlockDeviceMapping()創建個磁盤映射的對象，然後用BlockDeviceType()來創建磁盤對象，然後參數裏設置大小、類型、IOPS之類的，最後設置掛載映射和對應關係

import boto.ec2
from boto.ec2.blockdevicemapping import BlockDeviceMapping, BlockDeviceType

block_device_map = BlockDeviceMapping()
xvda = BlockDeviceType(delete_on_termination=True, size=12)
xvdb = BlockDeviceType(ephemeral_name='ephemeral0')
xvdf = BlockDeviceType(delete_on_termination=False, size=100, volume_type='gp2')
xvdg = BlockDeviceType(delete_on_termination=False, 
                       size=100, volume_type='io1', iops=1000)
block_device_map['/dev/xvda'] = xvda
block_device_map['/dev/sdb'] = xvdb
block_device_map['/dev/sdf'] = xvdf
block_device_map['/dev/sdg'] = xvdg

conn.run_instances(
    # other arguments
    block_device_map=block_device_map,
    # other arguments
    )