Pools

A pool is storage on one host. VM disks created in it live on that server’s disks.

Pools are per-host by nature. That is their limitation and their purpose: they are fast, simple and local.

Types

Type	Backed by	Notes
DIR	A directory on the host filesystem	The simplest. Disk images as files
LVM	An LVM volume group	Logical volumes as disks; less overhead than files
ZFS	A ZFS pool	Checksums, compression, snapshots at the filesystem
NFS	A mounted NFS export	Shared, if the export is reachable from several hosts
ISCSI	An attached iSCSI target	Shared block storage
CEPH	A replicated storage pool	Shared; see Replicated storage

Status

Status	Meaning
ACTIVE	Available
INACTIVE	Defined but not started
BUILDING	Being constructed
DEGRADED	Working with a fault — a failed disk in a mirror
ERROR	Unusable

A DEGRADED pool still serves data and is a warning, not an outage. Treat it as urgent anyway: degraded means the redundancy you were relying on is already spent.

The default pool

The installer creates a local pool at /var/lib/hyperion/vms on its own logical volume. VMs created without a specified backing land there.

It is a DIR pool on local disk, so anything in it is pinned to that host.

Creating a pool

From a host’s Storage tab in Infrastructure.

Directory pool — give it a name and a path.

LVM pool — choose from the host’s available disks. The screen lists disks that are genuinely free: not mounted, not already in a pool, not part of a mirror.

Warning — Building a pool on a disk destroys what is on it. The available-disks list excludes disks in obvious use, but it cannot know that a disk you attached last week has something you want.

Software mirrors

A host can mirror disks with a software RAID device, and build a pool on the result. Members can be added and removed, and the mirror can be torn down.

This gives redundancy against a single disk failing within a host. It is not a substitute for replication across hosts: a mirror does not survive the server.

Capacity

Each pool reports capacity, allocated and available. Usage is allocated against capacity.

Watch allocated rather than used. Thin-provisioned disks can be allocated well beyond what is physically present, and a pool that runs out of real space while its guests believe they have room fails in ways the guests handle badly.

Syncing

Pools can be re-read from the host, which reconciles what the platform believes with what is actually there. Use it after changing storage outside the platform, or when a pool’s reported state looks wrong.

Choosing a pool for a VM disk

The create-VM form offers the pools on the host or zone the VM will land on.

Choose a local pool when:

• the VM is disposable, or rebuilt from configuration,
• you want the lowest latency available,
• the deployment has no shared storage.

Choose shared backing when the VM needs to migrate or be restarted elsewhere — which is most production workloads.

Moving a VM off a pool

A VM’s disks can be moved between backings without recreating it. Use it to free a pool you intend to remove, or to make a pinned VM migratable.

It copies data and takes as long as the data takes. See Live migration.