centos 2.6.32-431,查看物理卷组，提示 No volume groups found，要怎么继续扩容
输入exit，退出lvm模式
创建卷组：
[root@localhost dev]# vgcreate centos /dev/sda4
Volume group "centos" successfully created
[root@localhost dev]# vgs
VG #PV #LV #SN Attr VSize VFree
centos 1 0 0 wz--n- 30.00g 30.00g
[root@localhost dev]# vgdisplay
--- Volume group ---
VG Name centos
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 1
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 0
Open LV 0
Max PV 0
Cur PV 1
Act PV 1
VG Size 30.00 GiB
PE Size 4.00 MiB
Total PE 7679
Alloc PE / Size 0 / 0
Free PE / Size 7679 / 30.00 GiB
VG UUID CtlAe0-K4P5-naeA-5q0t-t8kC-NBSm-GeytTN
再进入lvm模式，继续之后的操作