Chapter 7. Data Centers
7.1. Introduction to Data Centers
A data center is a logical entity that defines the set of resources used in a specific environment. A data center is considered a container resource, in that it is comprised of logical resources, in the form of clusters and hosts; network resources, in the form of logical networks and physical NICs; and storage resources, in the form of storage domains.
A data center can contain multiple clusters, which can contain multiple hosts; it can have multiple storage domains associated to it; and it can support multiple virtual machines on each of its hosts. A Red Hat Virtualization environment can contain multiple data centers; the data center infrastructure allows you to keep these centers separate.
All data centers are managed from the single Administration Portal.
Figure 7.1. Data Centers
Red Hat Virtualization creates a default data center during installation. You can configure the default data center, or set up new appropriately named data centers.
7.1.1. The Storage Pool Manager
The Storage Pool Manager (SPM) is a role given to one of the hosts in the data center enabling it to manage the storage domains of the data center. The SPM entity can be run on any host in the data center; the Red Hat Virtualization Manager grants the role to one of the hosts. The SPM does not preclude the host from its standard operation; a host running as SPM can still host virtual resources.
The SPM entity controls access to storage by coordinating the metadata across the storage domains. This includes creating, deleting, and manipulating virtual disks (images), snapshots, and templates, and allocating storage for sparse block devices (on SAN). This is an exclusive responsibility: only one host can be the SPM in the data center at one time to ensure metadata integrity.
The Red Hat Virtualization Manager ensures that the SPM is always available. The Manager moves the SPM role to a different host if the SPM host encounters problems accessing the storage. When the SPM starts, it ensures that it is the only host granted the role; therefore it will acquire a storage-centric lease. This process can take some time.
7.1.2. SPM Priority
The SPM role uses some of a host’s available resources. The SPM priority setting of a host alters the likelihood of the host being assigned the SPM role: a host with high SPM priority will be assigned the SPM role before a host with low SPM priority. Critical virtual machines on hosts with low SPM priority will not have to contend with SPM operations for host resources.
You can change a host’s SPM priority in the SPM tab in the Edit Host window.