Chapter 8. Storage

8.1. Introduction to Storage

A storage domain is a collection of images that have a common storage interface. A storage domain contains complete images of templates and virtual machines (including snapshots), ISO files, and metadata about themselves. A storage domain can be made of either block devices (SAN - iSCSI or FCP) or a file system (NAS - NFS, GlusterFS, or other POSIX compliant file systems).

There are two types of storage domains:

  • Data Domain: A data domain holds the virtual hard disks and OVF files of all the virtual machines and templates in a data center, and cannot be shared across data centers. Data domains of multiple types (iSCSI, NFS, FC, POSIX, and Gluster) can be added to the same data center, provided they are all shared, rather than local, domains.

    Important

    You must have one host with the status of Up and have attached a data domain to a data center before you can attach an ISO domain and an export domain.

  • ISO Domain: ISO domains store ISO files (or logical CDs) used to install and boot operating systems and applications for the virtual machines, and can be shared across different data centers. An ISO domain removes the data center’s need for physical media. ISO domains can only be NFS-based. Only one ISO domain can be added to a data center.
Important

If your host is booting from SAN storage and loses connectivity to the storage, the storage file systems become read-only and remain in this state after connectivity is restored.

To prevent this situation, Red Hat recommends adding a drop-in multipath configuration file for the boot LUN to ensure that it is queued when there is a connection:

# cat /etc/multipath/conf.d/host.conf
multipaths {
    multipath {
        wwid boot_LUN_wwid
        no_path_retry queue
    }

See the next section to attach existing FCP storage as a data domain. More storage options are available in the Administration Guide.