The {pve} 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 the future.
There are basically two different classes of storage types:
- File level storage
-
File level based storage technologies allow access to a fully featured (POSIX) file system. They are in general more flexible than any Block level storage (see below), and allow you to store content of any type. ZFS is probably the most advanced system, and it has full support for snapshots and clones.
- 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 and GlusterFS are distributed systems, replicating storage data to different nodes.
| Description | Plugin type | Level | Shared | Snapshots | Stable |
|---|---|---|---|---|---|
ZFS (local) |
|
both1 |
no |
yes |
yes |
Directory |
|
file |
no |
no2 |
yes |
BTRFS |
|
file |
no |
yes |
technology preview |
NFS |
|
file |
yes |
no2 |
yes |
CIFS |
|
file |
yes |
no2 |
yes |
Proxmox Backup |
|
both |
yes |
n/a |
yes |
GlusterFS |
|
file |
yes |
no2 |
yes |
CephFS |
|
file |
yes |
yes |
yes |
LVM |
|
block |
no3 |
no |
yes |
LVM-thin |
|
block |
no |
yes |
yes |
iSCSI/kernel |
|
block |
yes |
no |
yes |
iSCSI/libiscsi |
|
block |
yes |
no |
yes |
Ceph/RBD |
|
block |
yes |
yes |
yes |
ZFS over iSCSI |
|
block |
yes |
yes |
yes |
1: Disk images for VMs are stored in ZFS volume (zvol) datasets, which provide block device functionality.
2: On file based storages, snapshots are possible with the qcow2 format.
3: It is possible to use LVM on top of an iSCSI or FC-based storage.
That way you get a shared LVM storage
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 receive IO errors. 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. |
All {pve} 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 makes perfect sense for shared storage, because the same “shared” storage is accessible from all nodes. But it 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.
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> <property> ...
The <type>: <STORAGE_ID> line starts the pool definition, which is then
followed by a list of properties. Most properties require a value. Some have
reasonable defaults, in which 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 {pve} installer creates additional storage entries
depending on the storage type chosen at installation time.
/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
|
Caution
|
It is problematic to have multiple storage configurations pointing to the exact same underlying storage. Such an aliased storage configuration can lead to two different volume IDs (volid) pointing to the exact same disk image. {pve} expects that the images' volume IDs point to, are unique. Choosing different content types for aliased storage configurations can be fine, but is not recommended. |
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 what this storage is used for.
- images
-
QEMU/KVM VM images.
- rootdir
-
Allow to store container data.
- vztmpl
-
Container templates.
- backup
-
Backup files (
vzdump). - iso
-
ISO images
- snippets
-
Snippet files, for example guest hook scripts
- shared
-
Indicate that this is a single storage with the same contents on all nodes (or all listed in the nodes option). It will not make the contents of a local storage automatically accessible to other nodes, it just marks an already shared storage as such!
- disable
-
You can use this flag to disable the storage completely.
- maxfiles
-
Deprecated, please use
prune-backupsinstead. Maximum number of backup files per VM. Use0for unlimited. - prune-backups
-
Retention options for backups. For details, see Backup Retention.
- format
-
Default image format (
raw|qcow2|vmdk) - preallocation
-
Preallocation mode (
off|metadata|falloc|full) forrawandqcow2images on file-based storages. The default ismetadata, which is treated likeoffforrawimages. When using network storages in combination with largeqcow2images, usingoffcan help to avoid timeouts.
|
Warning
|
It is not advisable to use the same storage pool on different {pve} 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. |
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>
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.
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 (“{pve}
Storage Manager”), which is able to perform common storage management
tasks.
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> --content iso
List container templates
pvesm list <STORAGE_ID> --content vztmpl
Show file system path for a volume
pvesm path <VOLUME_ID>
Exporting the volume local:103/vm-103-disk-0.qcow2 to the file target.
This is mostly used internally with pvesm import.
The stream format qcow2+size is different to the qcow2 format.
Consequently, the exported file cannot simply be attached to a VM.
This also holds for the other formats.
pvesm export local:103/vm-103-disk-0.qcow2 qcow2+size target --with-snapshots 1