1.4. Storage
1.4. Storage Red Hat Virtualization uses a centralized storage system for virtual disks, templates, snapshots, and ISO files. Storage is logically grouped into storage pools, which are comprised of storage domains. A storage domain is a combination of storage capacity and metadata that describes the internal structure of the storage. There are three types of storage domain; data, export, and ISO. The data storage domain is the only one required by each data center. A data storage domain is exclusive to a single data center. Export and ISO domains are optional. Storage domains are shared resources, and must be accessible to all hosts in a data center. Storage networking can be implemented using Network File System (NFS), Internet Small Computer System Interface (iSCSI), GlusterFS, Fibre Channel Protocol (FCP), or any POSIX compliant networked filesystem. On NFS (and other POSIX-compliant filesystems) domains, all virtual disks, templates, and snapshots are simple files. On SAN (iSCSI/FCP) domains, block devices are aggregated by Logical Volume Manager (LVM)into a Volume Group (VG). Each virtual disk, template and snapshot is a Logical Volume (LV) on the VG. See the Red Hat Enterprise Linux Logical Volume Manager Administration Guide for more information on LVM. Data storage domain Data domains hold the virtual hard disk images of all the virtual machines running in the environment. Templates and snapshots of the virtual machines are also stored in the data domain. A data domain cannot be shared across data centers. Export storage domain An export domain is a temporary storage repository that is used to copy and move images between data centers and Red Hat Virtualization environments. The export domain can be used to back up virtual machines and templates. An export domain can be moved between data centers, but can only be active in one data center at a time. ISO storage domain ISO domains store ISO files, which are logical CD-ROMs used to install operating systems and applications for the virtual machines. As a logical entity that replaces a library of physical CD-ROMs or DVDs, an ISO domain removes the data center's need for physical media. An ISO domain can be shared across different data centers.