3.2.2 Shared Network Attached Storage (NFS)

Network Attached Storage – typically NFS – is a commonly used file-based storage system that is very suitable for the installation of Oracle VM storage repositories. Storage repositories contain various categories of resources such as templates, virtual disk images, ISO files and virtual machine configuration files, which are all stored as files in the directory structure on the remotely located, attached file system. Since most of these resources are rarely written to but are read frequently, NFS is ideal for storing these types of resources.

With Oracle VM you discover NFS storage via the server IP or host name and typically present storage to all the servers in a server pool to allow them to share the same resources. This, along with clustering, helps to enable high availability of your environment: virtual machines can be easily migrated between host servers for the purpose of load balancing or protecting important virtual machines from going off-line due to hardware failure.

NFS storage is exposed to Oracle VM Servers in the form of shares on the NFS server which are mounted onto the Oracle VM Server's file system. Since mounting an NFS share can be done on any server in the network segment to which NFS is exposed, it is possible not only to share NFS storage between servers of the same pool but also across different server pools.

In terms of performance, NFS is slower for virtual disk I/O compared to a logical volume or a raw disk. This is due mostly to its file-based nature. For better disk performance you should consider using block-based storage, which is supported in Oracle VM in the form of iSCSI or Fibre Channel SANs.

NFS can also be used to store server pool file systems for clustered server pools. This is the only shared storage facility that is supported for this purpose for SPARC-based server pools. In x86 environments, alternate shared storage such as iSCSI or Fibre Channel is generally preferred for this purpose for performance reasons.

Unsupported NFS Server Configurations

Oracle VM does not support the following configurations as they result in errors with storage repositories:

Multiple IP addresses or hostnames for one NFS server

If you assign multiple IP addresses or hostnames to the same NFS server, Oracle VM Manager treats each IP address or hostname as a separate NFS server.

DNS round-robin

If you configure your DNS so that a single hostname is assigned to multiple IP addresses, or a round-robin configuration, the storage repository is mounted repeatedly on the Oracle VM Server file system.

Nested NFS exports

If your NFS file system has other NFS file systems that reside inside the directory structure, or nested NFS exports, exporting the top level file directory from the NFS server results in an error where Oracle VM Server cannot access the storage repository. In this scenario, the OVMRU_002063E No utility server message is returned for certain jobs and written to AdminServer.log.

For more information about resolving errors with nested NFS exports, see Doc ID 2109556.1 in the Oracle Support Knowledge Base.