3.8 How is Storage Used for Server Pool Clustering?

To support server pool clustering, shared storage is required. On x86 hardware, this can be provided either in the form of an NFS share or a LUN on a SAN server. In either case, a disk image is created and formatted using OCFS2 (Oracle Cluster File System). On SPARC hardware, only NFS is supported to host the server pool file system.

For x86 environments, a clustered server pool always uses an OCFS2 file system to store the cluster configuration and to take advantage of OCFS2's heartbeat facility.

For SPARC environments, a clustered server pool is always hosted on an NFS share. Clustering for SPARC makes use of the same mechanisms that are available in OCFS2, but does not use the actual OCFS2 file system. Instead, clustering data is stored directly in the NFS share.

There are two types of heartbeats used within the cluster to ensure high availability:

  • The disk heartbeat: all Oracle VM Servers in the cluster write a time stamp to the server pool file system device.

  • The network heartbeat: all Oracle VM Servers communicate through the network to signal to each other that every cluster member is alive.

These heartbeat functions exist directly within the kernel and are fundamental to the clustering functionality that Oracle VM offers for server pools. It is very important to understand that the heartbeating functions can be disturbed by I/O-intensive operations on the same physical storage. For example, importing a template or cloning a virtual machine in a storage repository on the same NFS server where the server pool file system resides may cause a time-out in the heartbeat communication, which in turn leads to server fencing and reboot. To avoid unwanted rebooting, it is recommended that you choose a server pool file system location with sufficient and stable I/O bandwidth. Place server pool file systems on a separate NFS server or use a small LUN, if possible. For more information on setting up storage for a server pool file system, see Section 3.10, “Are there Guidelines for Configuring Storage?”.