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152 lines
4.2 KiB
Markdown
152 lines
4.2 KiB
Markdown
# Proxmox LVM Architecture and Concepts
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## 1. Overview of LVM
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Logical Volume Manager (LVM) provides a flexible storage management layer
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between physical disks and file systems. It allows administrators to allocate,
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resize, and manage storage dynamically, without the limitations of fixed disk
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partitions.
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The storage hierarchy under LVM is as follows:
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Physical Volume (PV) → Volume Group (VG) → Logical Volume (LV)
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Each layer abstracts the one beneath it to provide logical storage that can be
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managed independently of the physical disk structure.
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## 2. Core LVM Components
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a. Physical Volume (PV)
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A Physical Volume represents a raw storage device (such as a disk or a
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partition) that LVM can manage.
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It is initialized for use with the command:
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pvcreate /dev/sda2
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This prepares the partition /dev/sda2 as LVM-capable storage.
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b. Volume Group (VG)
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A Volume Group is a pool of storage composed of one or more Physical Volumes.
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It aggregates multiple disks or partitions into a single logical storage space.
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Example:
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vgcreate pve /dev/sda2
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In Proxmox, the default Volume Group created during installation is typically
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named pve. Once created, Logical Volumes can be allocated from this group.
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c. Logical Volume (LV)
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A Logical Volume functions like a virtual partition carved from a Volume Group.
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It behaves like a standard block device and can be formatted, mounted, or used
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for virtual machine disks.
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Example:
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lvcreate -L 50G -n vm-100-disk pve
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This command creates a 50 GB logical volume named vm-100-disk within the pve
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Volume Group.
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In Proxmox, each virtual machine disk backed by LVM appears as an LV under
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/dev/<VG>/, for example:
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/dev/pve/vm-100-disk-0
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d. Thin Pool and Thin Volumes
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A thin pool enables thin provisioning, which allows Logical Volumes to allocate
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physical space on demand rather than all at once.
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A thin pool is created as a special Logical Volume:
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lvcreate -L 500G -T pve/data
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Once the pool exists, thin-provisioned LVs can be created within it:
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lvcreate -V 100G -T pve/data -n vm-101-disk
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Here, vm-101-disk has a logical size of 100 GB but consumes physical space only
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as data is written. This is the mechanism used by Proxmox’s “LVM-Thin” storage
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type.
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## 3. Example: Creating an Extra LV for /var/lib/vz
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To create a new thin-provisioned LV for /var/lib/vz, the following command is used:
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lvcreate -n vz -V 10G pve/data
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Explanation:
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-n vz: Names the new LV “vz”.
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-V 10G: Defines a virtual (thin-provisioned) size of 10 GB.
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pve/data: Specifies that the LV should be created within the thin pool data
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inside the VG pve.
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This creates /dev/pve/vz, a 10 GB thin-provisioned LV that can then be formatted
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and mounted:
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mkfs.ext4 /dev/pve/vz
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mkdir /var/lib/vz
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mount /dev/pve/vz /var/lib/vz
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This approach isolates /var/lib/vz—commonly used by Proxmox to store container
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data, ISO images, and templates—from the root filesystem.
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4. Typical Proxmox LVM Layout
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A standard Proxmox installation configured with LVM uses a single Volume Group
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(pve) containing several Logical Volumes:
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/dev/sda (disk)
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└── /dev/sda2 (partition)
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└── PV → VG: pve
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├── LV: root → Mounted as /
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├── LV: swap → Used as swap space
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└── LV-Thin: data → Thin pool for VM and container disks
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├── Thin LV: vm-100-disk-0
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└── Thin LV: vm-101-disk-0
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This structure allows the operating system, swap, and virtual machine disks to
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share a single pool of storage while maintaining isolation through logical
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volumes.
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## 4. Example of Creating a new LVM thin pool and LV
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To create a new LVM thin pool and a thin-provisioned logical volume,
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follow these steps:
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1. **Create a Physical Volume (if not already done)**
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If you have a new disk or partition to use, initialize it as a Physical Volume:
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```bash
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pvcreate /dev/sdb1
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```
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2. **Create a Volume Group**
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Create a new Volume Group that includes the Physical Volume:
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```bash
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vgcreate backup /dev/sdb1
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```
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3. **Create a Thin Pool**
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Create a thin pool within the Volume Group:
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```bash
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lvcreate -L 200G -T backup/thinpool
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```
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4. Configure the thin pool to storage.cfg
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```
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lvmthin: backup-lvm
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thinpool backup/thinpool
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vgname backup
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content rootdir,images
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nodes proxmox-node1,proxmox-node2 # List of cluster nodes
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```
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