OpenStack 归档 - 虚拟机临时存储与块存储
总体来说，虚拟机内部的存储分临时存储与可拔插的块存储两部分，所谓临时存储既是指存储空间会随着虚拟机的创建而产生，删除而消亡。而块存储(volume)则可以将用户的数据保存下来，并可以attach到不通的虚机机上。
默认情况
默认情况创建一个虚机只有一个盘，mount到root分区，看下下面的例子。
nova boot default --image cirros-0.3.5-x86_64-disk --flavor m1.small --nic net-name=private
$ sudo fdisk -l
Disk /dev/vda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Device Boot Start End Blocks Id System
/dev/vda1 * 16065 41929649 20956792+ 83 Linux
$ df -h
Filesystem Size Used Available Use% Mounted on
/dev 998.3M 0 998.3M 0% /dev
/dev/vda1 23.2M 18.0M 4.0M 82% /
tmpfs 1001.8M 0 1001.8M 0% /dev/shm
tmpfs 200.0K 68.0K 132.0K 34% /run
$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 253:0 0 20G 0 disk
`-vda1 253:1 0 20G 0 part /
块设备
如果希望数据能持久的保存下来，即便虚拟机被删之后，还能找到在之前的数据，可以给虚拟机添加一个块设备。块设备由Cinder服务提供，可以将其理解为一块U盘，可以动态的拔插到的你的电脑上。如下，我们给虚拟机添加一个块设备volume。
再来看看虚拟机里的存储空间，我们会发现多出来一块盘。
$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 253:0 0 20G 0 disk
`-vda1 253:1 0 20G 0 part /
vdb 253:16 0 1G 0 disk
$ sudo fdisk -l
Disk /dev/vda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Device Boot Start End Blocks Id System
/dev/vda1 * 16065 41929649 20956792+ 83 Linux
Disk /dev/vdb: 1073 MB, 1073741824 bytes
16 heads, 63 sectors/track, 2080 cylinders, total 2097152 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Ephemeral 与Swap
另外，可以根据需要在虚拟机里创建一些临时的分区/盘，但这些盘同样会时随着虚拟机的生命周期消亡而消亡。
首先创建一个flavor,
$ nova flavor-create --ephemeral 20 --swap 512 testeph 7 512 1 1
+----+---------+-----------+------+-----------+------+-------+-------------+-----------+
| ID | Name | Memory_MB | Disk | Ephemeral | Swap | VCPUs | RXTX_Factor | Is_Public |
+----+---------+-----------+------+-----------+------+-------+-------------+-----------+
| 7 | testeph | 512 | 1 | 20 | 512 | 1 | 1.0 | True |
+----+---------+-----------+------+-----------+------+-------+-------------+-----------+
根据此flavor创建一个虚拟机:
$ nova boot --image cirros-0.3.5-x86_64-disk --flavor 7 --nic net-name=private --ephemeral size=1 emph1
$ sudo fdisk -l
Disk /dev/vda: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders, total 2097152 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Device Boot Start End Blocks Id System
/dev/vda1 * 16065 2088449 1036192+ 83 Linux
Disk /dev/vdb: 1073 MB, 1073741824 bytes
16 heads, 63 sectors/track, 2080 cylinders, total 2097152 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/vdb doesn't contain a valid partition table
Disk /dev/vdc: 536 MB, 536870912 bytes
16 heads, 63 sectors/track, 1040 cylinders, total 1048576 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 253:0 0 1G 0 disk
`-vda1 253:1 0 1011.9M 0 part /
vdb 253:16 0 1G 0 disk /mnt
vdc 253:32 0 512M 0 disk
可以看出，swap和ephemeral 是以独立的虚拟磁盘来呈现的。disk.eph0 与 disk.swap 都存放在虚拟机的目录下，这意味着虚拟机删除之后，这些文件也将随之被删除。
$ ls /opt/stack/data/nova/instances/29cc9a74-bebc-429d-a0b8-58fbfe89b2cd
console.log disk disk.eph0 disk.info disk.swap
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