Block Device Mapping

关于创建实例的时候添加各种磁盘以及其他设置的boto使用方法，下面给个例子
一般建议字母A用作根分区，B到E用做实例存储（InstanceStore，ephemeral），F以后用作EBS, 只是个规范建议，非不这么搞也行
基本是先用BlockDeviceMapping()创建个磁盘映射的对象，然后用BlockDeviceType()来创建磁盘对象，然后参数里设置大小、类型、IOPS之类的，最后设置挂载映射和对应关系

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
    )