给KVM虚拟机增加硬盘

1. host增加物理硬盘并分区

HOST作为KVM的宿主计算机，管理所有GUEST虚拟机。我们通过给HOST增加物理硬盘，然后分给GUEST，从而实现给虚拟机硬盘扩容的效果。

如何给计算机增加物理硬盘并分区，请参考：多硬盘分区管理fdisk 文章

查看HOST机的硬盘

~ sudo fdisk -l Disk /dev/sda: 299.4 GB, 299439751168 bytes
255 heads, 63 sectors/track, 36404 cylinders, total 584843264 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: 0x000efd7c

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1            2048    97656831    48827392   82  Linux swap / Solaris
/dev/sda2        97656832   136718335    19530752   83  Linux
/dev/sda3       136718336   214843335    39062500   83  Linux
/dev/sda4   *   214843392   215037951       97280   83  Linux Disk /dev/sdb: 1999.3 GB, 1999307276288 bytes
255 heads, 63 sectors/track, 243068 cylinders, total 3904897024 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: 0xf919a976

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048  1952448511   976223232    7  HPFS/NTFS/exFAT
/dev/sdb2      1952448512  3904897023   976224256    5  Extended
/dev/sdb5      1952450560  2267023360   157286400+  83  Linux
/dev/sdb6      2267025409  2581596160   157285376   83  Linux
/dev/sdb7      2581598209  2896168960   157285376   83  Linux
/dev/sdb8      2896171009  3210741760   157285376   83  Linux
/dev/sdb9      3210743809  3525314560   157285376   83  Linux
/dev/sdb10     3525316609  3904897023   189790207+  83  Linux

~ df -h Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3        37G  3.4G   32G  10% /
udev             24G  4.0K   24G   1% /dev
tmpfs           9.5G  1.1M  9.5G   1% /run
none            5.0M  8.0K  5.0M   1% /run/lock
none             24G  152K   24G   1% /run/shm
none            100M   28K  100M   1% /run/user
cgroup           24G     0   24G   0% /sys/fs/cgroup
/dev/sda2        19G  3.6G   14G  21% /home
/dev/sda4        92M   34M   54M  39% /boot
/dev/sdb1       931G  100G  832G  11% /disk/sdb1
/dev/sdb6       148G  188M  140G   1% /disk/sdb6

下面将进行两个测试：
通过virsh给guest增加文件硬盘：通过文件硬盘的镜像/disk/sdb6/c1d6.img
通过virsh给guest增加分区硬盘：直接使用分区硬盘/dev/sdb5

2. 通过virsh给guest增加文件硬盘

创建文件硬盘的镜像

~ cd /disk/sdb6/
~ sudo qemu-img create -f raw /disk/sdb6/c1d6.img 10G Formatting '/disk/sdb6/c1d6.img', fmt=raw size=10737418240

~ ls -l
-rw-r--r-- 1 root root 10737418240 Jul  8 16:37 c1d6.img
drwx------ 2 root root       16384 Jul  8 09:03 lost+found/

通过virsh管理工具加载硬盘

~ sudo virsh Welcome to virsh, the virtualization interactive terminal.
Type:  'help' for help with commands
       'quit' to quit

#查看系统内的虚拟机 virsh # list Id Name State
----------------------------------------------------
5 server3 running
6 server4 running
7 d2 running
8 r1 running
9 server2 running
12 c1 running

#在这里我们要对c1进行硬盘扩容 virsh # edit c1 #找到硬盘配置(原来的系统硬盘)







#增加文件硬盘,vdb

 cache='none'/>  
'0x06' function='0x0'/>


#保存退出

重启c1虚拟机

#请使用destroy命令，reboot和shutdown不管用。
~ virsh # destroy c1
Domain c1 destroyed

#list找不到c1 
~ virsh # list
 Id    Name                           State
----------------------------------------------------
 5     server3                        running
 6     server4                        running
 7     d2                             running
 8     r1                             running
 9     server2                        running

#启动虚拟机c1
~ virsh # start c1
Domain c1 started

#进入虚拟机c1
~ console c1 

在c1中，进行硬盘查检并分区

~ sudo fdisk -l Disk /dev/vda: 42.9 GB, 42949672960 bytes
16 heads, 63 sectors/track, 83220 cylinders, total 83886080 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: 0x000516aa

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048      499711      248832   83  Linux
/dev/vda2          501758    83884031    41691137    5  Extended
/dev/vda5          501760    83884031    41691136   8e  Linux LVM Disk /dev/vdb: 10.7 GB, 10737418240 bytes
16 heads, 63 sectors/track, 20805 cylinders, total 20971520 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/mapper/u1210-root: 38.4 GB, 38394658816 bytes
255 heads, 63 sectors/track, 4667 cylinders, total 74989568 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/mapper/u1210-root doesn't contain a valid partition table

Disk /dev/mapper/u1210-swap_1: 4294 MB, 4294967296 bytes
255 heads, 63 sectors/track, 522 cylinders, total 8388608 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/mapper/u1210-swap_1 doesn't contain a valid partition table

/dev/vdb已经被识别，接下来 分区,格式化,挂载,使用

硬盘分区

~ sudo fdisk /dev/vdb Command (m for help): p

Disk /dev/vdb: 161.1 GB, 161061274112 bytes
16 heads, 63 sectors/track, 312076 cylinders, total 314572801 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: 0x3b49c6a0

   Device Boot      Start         End      Blocks   Id  System

Command (m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
Partition number (1-4, default 1):
Using default value 1
First sector (2048-314572800, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-314572800, default 314572800):
Using default value 314572800

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

#分区生效
~ sudo partprobe ~ sudo fdisk -l
Disk /dev/vdb: 10.7 GB, 10737418240 bytes
2 heads, 17 sectors/track, 616809 cylinders, total 20971520 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: 0xf0432cd6

   Device Boot      Start         End      Blocks   Id  System
/dev/vdb1            2048    20971519    10484736   83  Linux

格式化

~ sudo mkfs -t ext4 /dev/vdb1 mke2fs 1.42.5 (29-Jul-2012)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
9830400 inodes, 39321344 blocks
1966067 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
1200 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
        4096000, 7962624, 11239424, 20480000, 23887872

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

挂载

~ sudo mount /dev/vdb1 /home/cos/hadoopb ~ df -h
Filesystem              Size  Used Avail Use% Mounted on
/dev/mapper/u1210-root   36G  1.1G   33G   4% /
udev                    2.0G  4.0K  2.0G   1% /dev
tmpfs                   791M  232K  791M   1% /run
none                    5.0M     0  5.0M   0% /run/lock
none                    2.0G     0  2.0G   0% /run/shm
none                    100M     0  100M   0% /run/user
/dev/vda1               228M   29M  188M  14% /boot
/dev/vdb1               9.9G  151M  9.2G   2% /home/cos/hadoopb

使用
/home/cos/hadoopb的目录，已经挂载到了/dev/vdb1上面，我可以在hadoopb下载做任何的操作。

3. 通过virsh给guest增加分区硬盘

直接使用HOST的分区硬盘/dev/sdb5，做个虚拟机c1的分区

virsh # edit c1

#新增新硬盘vbc

cache='none'/>  ='vbc' bus='virtio'/>


virsh # destroy c1
Domain c1 destroyed virsh # start c1 Domain c1 started

virsh # console c1

登陆虚拟c1，查看硬盘信息

sudo fdisk -l [sudo] password for cos: Disk /dev/vda: 42.9 GB, 42949672960 bytes
16 heads, 63 sectors/track, 83220 cylinders, total 83886080 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: 0x000516aa

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048      499711      248832   83  Linux
/dev/vda2          501758    83884031    41691137    5  Extended
/dev/vda5          501760    83884031    41691136   8e  Linux LVM Disk /dev/vdb: 10.7 GB, 10737418240 bytes
2 heads, 17 sectors/track, 616809 cylinders, total 20971520 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: 0xf0432cd6

   Device Boot      Start         End      Blocks   Id  System
/dev/vdb1            2048    20971519    10484736   83  Linux Disk /dev/vdc: 161.1 GB, 161061274112 bytes
4 heads, 4 sectors/track, 19660800 cylinders, total 314572801 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: 0x3b49c6a0

   Device Boot      Start         End      Blocks   Id  System
/dev/vdc1            2048   314572800   157285376+  83  Linux

Disk /dev/mapper/u1210-root: 38.4 GB, 38394658816 bytes
255 heads, 63 sectors/track, 4667 cylinders, total 74989568 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/mapper/u1210-root doesn't contain a valid partition table

Disk /dev/mapper/u1210-swap_1: 4294 MB, 4294967296 bytes
255 heads, 63 sectors/track, 522 cylinders, total 8388608 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/mapper/u1210-swap_1 doesn't contain a valid partition table

已经被正确识别
Disk /dev/vdc: 161.1 GB, 161061274112 bytes

接下来，可以参考上面类似的过程，分区，格式化，挂载，使用。

我们直接使用硬件分区，比分区的映射文件会更有效果。

kvm 虚拟机的磁盘大小可通过命令：

qemu-img resize filename size 来改，要注意的是resize只支持raw格式的磁盘文件，

如果想更改qcow2等格式的磁盘大小，需先用qemu-img convert 转换磁盘格式后才能更改大小；另外，用命令改完大小后需重启kvm虚拟机，系统才能识别新添加的磁盘容量。

                              更改kvm虚拟机磁盘大小 

1、用qemu-img resize更改磁盘大小 
以xp为例，原来磁盘的大小为100M，更改为250M
[root@kvmserver ]# qemu-img info xp_4_test.disk01
image: xp_4_test.disk01
file format: raw
virtual size: 99M (100000000 bytes)
disk size: 54M
[root@kvmserver]# qemu-img resize xp_4_test.disk01 +150M //更改大小
Image resized.
[root@kvmserver]# qemu-img info xp_4_test.disk01
image: xp_4_test.disk01
file format: raw
virtual size: 250M (262144000 bytes)　//可以看到大小已更改为250M
disk size: 54M
2、重启kvm虚拟机
[root@kvmserver ]# virsh shutdown xp_4_test

                                               KVM磁盘性能优化

磁盘性能是虚拟技术中的一个瓶颈，虚拟机由于经过封装以后，磁盘有所下降，尤其要对磁盘性能进行优化。

优化要点：

1、在母机（host）上，设置磁盘调度器为 deadline，有两种方法

– 在启动的时候，加入参数（需要重新启动）：
elevator=deadline

– 或者实时调整参数（不需要重新启动，但是下次启动时丢失）：
for f in /sys/block/sd*/queue/scheduler; do echo “deadline” > $f; done

2、使用 virtio，一定注意，否则导致磁盘性能严重下降

3、在虚拟机（VM）上，设置磁盘调度器为 noop，有两种方法

– 在启动的时候，加入参数（需要重新启动）：
elevator=noop

– 或者实时调整参数（不需要重新启动，但是下次启动时丢失）：
for f in /sys/block/sd*/queue/scheduler; do echo “noop” > $f; done

4、尽量使用 LVM 作为虚拟机的磁盘，qcow2会带来额外的负担，从而导致IO性能下降

 5、注意虚拟机内的 virtio驱动程序一定是最新的，特别是windows虚拟机

参考：