Linux LVM

What’s LVM? Why using Linux Logical Volume Manager or LVM? Well, these questions are not the scope here. But in brief, the most attractive feature of Logical Volume Manager is to make disk management easier in Linux!

Basically, LVM allows users to dynamically extend or shrink Linux 「partition」 or file system in online mode! The LVM can resize volume groups (VG) online by adding new physical volumes (PV) or rejecting those existing PVs attached to VG.

A visualized concept diagram of the Linux Logical Volume Manager or LVM

LVM 術語介紹

1. 物理存儲介質（The physical media）：這裏指系統的存儲設備：硬盤，如：/dev/hda一、/dev/sda等等，是存儲系統最低層的存儲單元.
2. 物理卷（physical volume）：物理卷就是指硬盤分區或從邏輯上與磁盤分區具備一樣功能的設備(如RAID)，是LVM的基本存儲邏輯塊，但和基本的物理存儲介質（如分區、磁盤等）比較，卻包含有與LVM相關的管理參數。
3. 卷組（Volume Group）：LVM卷組相似於非LVM系統中的物理硬盤，其由物理卷組成。能夠在卷組上建立一個或多個「LVM分區」（邏輯卷），LVM卷組由一個或多個物理卷組成。
4. 邏輯卷（logical volume）：LVM的邏輯卷相似於非LVM系統中的硬盤分區，在邏輯卷之上能夠創建文件系統(好比/home或者/usr等)
5. PE（physical extent）：每個物理卷被劃分爲稱爲PE(Physical Extents)的基本單元，具備惟一編號的PE是能夠被LVM尋址的最小單元。PE的大小是可配置的，默認爲4MB

Setup Linux LVM

Using the whole secondary hard disk for LVM partition: fdisk /dev/sda
At the Linux fdisk command prompt

1. press n to create a new disk partition,
2. press p to create a primary disk partition,
3. press 1 to denote it as 1st disk partition,
4. press ENTER twice to accept the default of 1st and last cylinder – to convert the whole secondary hard disk to a single disk partition,
5. press t (will automatically select the only partition – partition 1) to change the default Linux partition type (0×83) to LVM partition type (0x8e),
6. press L to list all the currently supported partition type,
7. press 8e (as per the L listing) to change partition 1 to 8e, i.e. Linux LVM partition type,
8. press p to display the secondary hard disk partition setup. Please take note that the first partition is denoted as /dev/sda1 in Linux,
9. press w to write the partition table and exit fdisk upon completion.

fdisk end!

This LVM command will create a LVM physical volume (PV) on a regular hard disk or partition: pvcreate /dev/sda1

Now, another LVM command to create a LVM volume group (VG) called vg0 with a physical extent size (PE size) of 16MB: vgcreate -s 16M vg0 /dev/sda1

Be properly planning ahead of PE size before creating a volume group with vgcreate -s option!

Create a 400MB logical volume (LV) called lvol0 on volume group vg0: lvcreate -L 400M -n lvol0 vg0

This lvcreate command will create a softlink /dev/vg0/lvol0 point to a correspondence block device file called /dev/mapper/vg0-lvol0.

The Linux LVM setup is almost done. Now is the time to format logical volume lvol0 to create a Red Hat Linux supported file system, i.e. EXT3 file system, with 1% reserved block count: mkfs -t ext3 -m 1 -v /dev/mapper/vg0-lvol0

Create a mount point before mounting the new EXT3 file system: mkdir /mnt/vfs

The last step of this LVM tutorial – mount the new EXT3 file system created on logical volume lvol0 of LVM to /mnt/vfs mount point: mount -t ext3 /dev/mapper/vg0-lvol0 /mnt/vfs

To confirm the LVM setup has been completed successfully, use df -h command.

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摘自

http://www.walkernews.net/2007/07/02/how-to-create-linux-lvm-in-3-minutes/