7.1. Storage Types

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.

Table 7.1. Available storage types

Description PVE type Level SharedSnapshotsStable

ZFS (local)

zfspool

file

no

yes

yes

Directory

dir

file

no

no1

yes

BTRFS

btrfs

file

no

yes

technology preview

NFS

nfs

file

yes

no1

yes

CIFS

cifs

file

yes

no1

yes

Proxmox Backup

pbs

both

yes

n/a

yes

GlusterFS

glusterfs

file

yes

no1

yes

CephFS

cephfs

file

yes

yes

yes

LVM

lvm

block

no2

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

ZFS over iSCSI

zfs

block

yes

yes

yes

1: On file based storages, snapshots are possible with the qcow2 format.

2: 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.