Storage

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The Proxmox VE storage model is very flexible. Virtual machine images can either be stored on one or several local storages, or on shared storage like NFS or iSCSI (NAS, SAN). There are no limits, and you may configure as many storage pools as you like. You can use all storage technologies available for Debian Linux.

One major benefit of storing VMs on shared storage is the ability to live-migrate running machines without any downtime, as all nodes in the cluster have direct access to VM disk images. There is no need to copy VM image data, so live migration is very fast in that case.

The storage library (package libpve-storage-perl) uses a flexible plugin system to provide a common interface to all storage types. This can be easily adopted to include further storage types in future.

Storage Types

There are basically two different classes of storage types:

Block level storage

Allows to store large raw images. It is usually not possible to store other files (ISO, backups, ..) on such storage types. Most modern block level storage implementations support snapshots and clones. RADOS, Sheepdog and GlusterFS are distributed systems, replicating storage data to different nodes.

File level storage

They allow access to a full featured (POSIX) file system. They are more flexible, and allows you to store any content type. ZFS is probably the most advanced system, and it has full support for snapshots and clones.

Table 1. Available storage types
Description PVE type Level Shared Snapshots Stable

ZFS (local)

zfspool

file

no

yes

yes

Directory

dir

file

no

no

yes

NFS

nfs

file

yes

no

yes

GlusterFS

glusterfs

file

yes

no

yes

LVM

lvm

block

no

no

yes

LVM-thin

lvmthin

block

no

yes

yes

iSCSI/kernel

iscsi

block

yes

no

yes

iSCSI/libiscsi

iscsidirect

block

yes

no

yes

Ceph/RBD

rbd

block

yes

yes

yes

Sheepdog

sheepdog

block

yes

yes

beta

ZFS over iSCSI

zfs

block

yes

yes

yes

Tip It is possible to use LVM on top of an iSCSI storage. That way you get a shared LVM storage.

Thin Provisioning

A number of storages, and the Qemu image format qcow2, support thin provisioning. With thin provisioning activated, only the blocks that the guest system actually use will be written to the storage.

Say for instance you create a VM with a 32GB hard disk, and after installing the guest system OS, the root file system of the VM contains 3 GB of data. In that case only 3GB are written to the storage, even if the guest VM sees a 32GB hard drive. In this way thin provisioning allows you to create disk images which are larger than the currently available storage blocks. You can create large disk images for your VMs, and when the need arises, add more disks to your storage without resizing the VMs' file systems.

All storage types which have the “Snapshots” feature also support thin provisioning.

Caution If a storage runs full, all guests using volumes on that storage receives IO error. This can cause file system inconsistencies and may corrupt your data. So it is advisable to avoid over-provisioning of your storage resources, or carefully observe free space to avoid such conditions.

Storage Configuration

All Proxmox VE related storage configuration is stored within a single text file at /etc/pve/storage.cfg. As this file is within /etc/pve/, it gets automatically distributed to all cluster nodes. So all nodes share the same storage configuration.

Sharing storage configuration make perfect sense for shared storage, because the same “shared” storage is accessible from all nodes. But is also useful for local storage types. In this case such local storage is available on all nodes, but it is physically different and can have totally different content.

Storage Pools

Each storage pool has a <type>, and is uniquely identified by its <STORAGE_ID>. A pool configuration looks like this:

<type>: <STORAGE_ID>
        <property> <value>
        <property> <value>
        ...

The <type>: <STORAGE_ID> line starts the pool definition, which is then followed by a list of properties. Most properties have values, but some of them come with reasonable default. In that case you can omit the value.

To be more specific, take a look at the default storage configuration after installation. It contains one special local storage pool named local, which refers to the directory /var/lib/vz and is always available. The Proxmox VE installer creates additional storage entries depending on the storage type chosen at installation time.

Default storage configuration (/etc/pve/storage.cfg)
dir: local
        path /var/lib/vz
        content iso,vztmpl,backup

# default image store on LVM based installation
lvmthin: local-lvm
        thinpool data
        vgname pve
        content rootdir,images

# default image store on ZFS based installation
zfspool: local-zfs
        pool rpool/data
        sparse
        content images,rootdir

Common Storage Properties

A few storage properties are common among different storage types.

nodes

List of cluster node names where this storage is usable/accessible. One can use this property to restrict storage access to a limited set of nodes.

content

A storage can support several content types, for example virtual disk images, cdrom iso images, container templates or container root directories. Not all storage types support all content types. One can set this property to select for what this storage is used for.

images

KVM-Qemu VM images.

rootdir

Allow to store container data.

vztmpl

Container templates.

backup

Backup files (vzdump).

iso

ISO images

shared

Mark storage as shared.

disable

You can use this flag to disable the storage completely.

maxfiles

Maximum number of backup files per VM. Use 0 for unlimited.

format

Default image format (raw|qcow2|vmdk)

Warning It is not advisable to use the same storage pool on different Proxmox VE clusters. Some storage operation need exclusive access to the storage, so proper locking is required. While this is implemented within a cluster, it does not work between different clusters.

Volumes

We use a special notation to address storage data. When you allocate data from a storage pool, it returns such a volume identifier. A volume is identified by the <STORAGE_ID>, followed by a storage type dependent volume name, separated by colon. A valid <VOLUME_ID> looks like:

local:230/example-image.raw
local:iso/debian-501-amd64-netinst.iso
local:vztmpl/debian-5.0-joomla_1.5.9-1_i386.tar.gz
iscsi-storage:0.0.2.scsi-14f504e46494c4500494b5042546d2d646744372d31616d61

To get the file system path for a <VOLUME_ID> use:

pvesm path <VOLUME_ID>

Volume Ownership

There exists an ownership relation for image type volumes. Each such volume is owned by a VM or Container. For example volume local:230/example-image.raw is owned by VM 230. Most storage backends encodes this ownership information into the volume name.

When you remove a VM or Container, the system also removes all associated volumes which are owned by that VM or Container.

Using the Command Line Interface

It is recommended to familiarize yourself with the concept behind storage pools and volume identifiers, but in real life, you are not forced to do any of those low level operations on the command line. Normally, allocation and removal of volumes is done by the VM and Container management tools.

Nevertheless, there is a command line tool called pvesm (“Proxmox VE Storage Manager”), which is able to perform common storage management tasks.

Examples

Add storage pools

pvesm add <TYPE> <STORAGE_ID> <OPTIONS>
pvesm add dir <STORAGE_ID> --path <PATH>
pvesm add nfs <STORAGE_ID> --path <PATH> --server <SERVER> --export <EXPORT>
pvesm add lvm <STORAGE_ID> --vgname <VGNAME>
pvesm add iscsi <STORAGE_ID> --portal <HOST[:PORT]> --target <TARGET>

Disable storage pools

pvesm set <STORAGE_ID> --disable 1

Enable storage pools

pvesm set <STORAGE_ID> --disable 0

Change/set storage options

pvesm set <STORAGE_ID> <OPTIONS>
pvesm set <STORAGE_ID> --shared 1
pvesm set local --format qcow2
pvesm set <STORAGE_ID> --content iso

Remove storage pools. This does not delete any data, and does not disconnect or unmount anything. It just removes the storage configuration.

pvesm remove <STORAGE_ID>

Allocate volumes

pvesm alloc <STORAGE_ID> <VMID> <name> <size> [--format <raw|qcow2>]

Allocate a 4G volume in local storage. The name is auto-generated if you pass an empty string as <name>

pvesm alloc local <VMID> '' 4G

Free volumes

pvesm free <VOLUME_ID>
Warning This really destroys all volume data.

List storage status

pvesm status

List storage contents

pvesm list <STORAGE_ID> [--vmid <VMID>]

List volumes allocated by VMID

pvesm list <STORAGE_ID> --vmid <VMID>

List iso images

pvesm list <STORAGE_ID> --iso

List container templates

pvesm list <STORAGE_ID> --vztmpl

Show file system path for a volume

pvesm path <VOLUME_ID>