1.LVM的基本概念
physical volume (PV)
通常是一快硬盘。相当于一个物理设备，磁盘空间物理卷PV。
volume group (VG)
相当于LVM的卷组，属于一个抽象下的组概念，一个VG可以包括多个PV。我的实操是我的VG下面，包含了PV(/dev/sda5)和PV(/dev/sdb1)如下:
root@linuxidc.com:~# pvdisplay
--- Physical volume ---
PV Name /dev/sda5
VG Name linuxidc.com-vg
PV Size 49.76 GiB / not usable 2.00 MiB
Allocatable yes (but full)
PE Size 4.00 MiB
Total PE 12738
Free PE 0
Allocated PE 12738
PV UUID ADh3K6-fjVA-5lLY-9vzu-eIxe-utiL-pOYtZa
--- Physical volume ---
PV Name /dev/sdb1
VG Name linuxidc.com-vg
PV Size 16.00 GiB / not usable 3.00 MiB
Allocatable yes (but full)
PE Size 4.00 MiB
Total PE 4095
Free PE 0
Allocated PE 4095
PV UUID 2RwFCw-lLul-8CIf-gHvb-0rC1-U0aG-SfHZGd
root@linuxidc.com:~# pvs
PV VG Fmt Attr PSize PFree
/dev/sda5 linuxidc.com-vg lvm2 a-- 49.76g 0
/dev/sdb1 linuxidc.com-vg lvm2 a-- 16.00g 0
logical volume (LV)
LV简单的理解是可以挂载到分区下的磁盘空间了。如下 :根分区/下的空间，代表着root这个lv。
root@linuxidc.com:~# lvs
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert
root linuxidc.com-vg -wi-ao--- 53.76g
swap_1 linuxidc.com-vg -wi-ao--- 12.00g
2.lvm扩展根目录分区的实战
2.1 设置硬盘/dev/sdb为linux lvm
先决条件:在vmware虚拟化平台下，我先添加了一块/dev/sdb的硬盘，并把硬盘设置为linux lvm,操作如下:
root@linuxidc.com:~# fdisk /dev/sdb
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x502d7728.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Command (m for help): p
Disk /dev/sdb: 17.2 GB, 17179869184 bytes
255 heads, 63 sectors/track, 2088 cylinders, total 33554432 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: 0x502d7728
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 (2048-33554431, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-33554431, default 33554431):
Using default value 33554431
Command (m for help): p
Disk /dev/sdb: 17.2 GB, 17179869184 bytes
255 heads, 63 sectors/track, 2088 cylinders, total 33554432 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: 0x502d7728
Device Boot Start End Blocks Id System
/dev/sdb1 2048 33554431 16776192 83 Linux
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): L