Chapter 11. Storage
Red Hat Virtualization uses a centralized storage system for virtual disks, ISO files and snapshots. Storage networking can be implemented using:
- Network File System (NFS)
- GlusterFS exports
- Other POSIX compliant file systems
- Internet Small Computer System Interface (iSCSI)
- Local storage attached directly to the virtualization hosts
- Fibre Channel Protocol (FCP)
- Parallel NFS (pNFS)
Setting up storage is a prerequisite for a new data center because a data center cannot be initialized unless storage domains are attached and activated.
As a Red Hat Virtualization system administrator, you need to create, configure, attach and maintain storage for the virtualized enterprise. You should be familiar with the storage types and their use. Read your storage array vendor’s guides, and see the Red Hat Enterprise Linux Storage Administration Guide for more information on the concepts, protocols, requirements or general usage of storage.
To add storage domains you must be able to successfully access the Administration Portal, and there must be at least one host connected with a status of Up.
Red Hat Virtualization has three 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. In addition, snapshots of the virtual machines are also stored in the data domain.
The data domain 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.
You must attach a data domain to a data center before you can attach domains of other types to it.
- ISO Domain: ISO domains store ISO files (or logical CDs) used to install and boot operating systems and applications for the virtual machines. An ISO domain removes the data center’s need for physical media. An ISO domain can be shared across different data centers. ISO domains can only be NFS-based. Only one ISO domain can be added to a data center.
Export Domain: Export domains are temporary storage repositories that are used to copy and move images between data centers and Red Hat Virtualization environments. Export domains can be used to backup virtual machines. An export domain can be moved between data centers, however, it can only be active in one data center at a time. Export domains can only be NFS-based. Only one export domain can be added to a data center.
NoteThe export storage domain is deprecated. Storage data domains can be unattached from a data center and imported to another data center in the same environment, or in a different environment. Virtual machines, floating virtual disks, and templates can then be uploaded from the imported storage domain to the attached data center. See Section 11.7, “Importing Existing Storage Domains” for information on importing storage domains.
Only commence configuring and attaching storage for your Red Hat Virtualization environment once you have determined the storage needs of your data center(s).
11.1. Understanding Storage Domains
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), or ISO files. A storage domain can be made of block devices (SAN - iSCSI or FCP) or a file system (NAS - NFS, GlusterFS, or other POSIX compliant file systems).
By default, GlusterFS domains and local storage domains support 4K block size. 4K block size can provide better performance, especially when using large files, and it is also necessary when you use tools that require 4K compatibility, such as VDO.
On NFS, all virtual disks, templates, and snapshots are files.
On SAN (iSCSI/FCP), each virtual disk, template or snapshot is a logical volume. Block devices are aggregated into a logical entity called a volume group, and then divided by LVM (Logical Volume Manager) into logical volumes for use as virtual hard disks. See Red Hat Enterprise Linux Logical Volume Manager Administration Guide for more information on LVM.
Virtual disks can have one of two formats, either QCOW2 or raw. The type of storage can be sparse or preallocated. Snapshots are always sparse but can be taken for disks of either format.
Virtual machines that share the same storage domain can be migrated between hosts that belong to the same cluster.
