SPARC: Guidelines for Sun Logical Domains in a Cluster

Consider the following points when you create a Sun Logical Domains (LDoms) I/O domain or guest domain on a physically clustered machine that is SPARC hypervisor capable:

• SCSI LUN requirement – The virtual shared storage device, or virtual disk back end, of a Sun LDoms guest domain must be a full SCSI LUN in the I/O domain. You cannot use an arbitrary virtual device.

• Fencing – Do not export a storage LUN to more than one guest domain on the same physical machine, unless you also disable fencing for that device. Otherwise, if two different guest domains on the same machine both are visible to a device, the device will be fenced whenever one of the guest domains dies. The fencing of the device will panic any other guest domain that subsequently tries to access the device.

• Network isolation – Guest domains that are located on the same physical machine but are configured in different clusters must be network isolated from each other. Use one of the following methods:

  • Configure the clusters to use different network interfaces in the I/O domain for the private network.

  • Use different network addresses for each of the clusters.

• Networking in guest domains – Network packets to and from guest domains must traverse service domains to reach the network drivers through virtual switches. Virtual switches use kernel threads that run at system priority. The virtual-switch threads must be able to acquire needed CPU resources to perform critical cluster operations, including heartbeats, membership, checkpoints, and so forth. Configuring virtual switches with the mode=sc setting enables expedited handling of cluster heartbeat packets. However, the reliability of other critical cluster operations can be enhanced by adding more CPU resources to the service domain under the following workloads:

  • High-interrupt load, for example, due to network or disk I/O. Under extreme load, virtual switches can preclude system threads from running for a long time, including virtual-switch threads.

  • Real-time threads that are overly aggressive in retaining CPU resources. Real-time threads run at a higher priority than virtual-switch threads, which can restrict CPU resources for virtual-switch threads for an extended time.

• Non-shared storage - On the Solaris 10 OS, for non-shared storage, such as for LDoms guest-domain OS images, you can use any type of virtual device. You can back such virtual devices by any implement in the I/O domain, such as files or volumes. However, do not copy files or clone volumes in the I/O domain for the purpose of mapping them into different guest domains of the same cluster. Such copying or cloning would lead to problems because the resulting virtual devices would have the same device identity in different guest domains. Always create a new file or device in the I/O domain, which would be assigned a unique device identity, then map the new file or device into a different guest domain.

• Exporting storage from I/O domains – If you configure a cluster that is composed of Sun Logical Domains I/O domains, do not export its storage devices to other guest domains that also run Sun Cluster software.

• Solaris I/O multipathing – Do not run Solaris I/O multipathing software (MPxIO) from guest domains. Instead, run Solaris I/O multipathing software in the I/O domain and export it to the guest domains.

• Private-interconnect IP address range – The private network is shared by all guest domains that are created on the same physical machine and it is visible to all these domains. Before you specify a private-network IP address range to the scinstall utility for use by a guest-domain cluster, ensure that the address range is not already in use by another guest domain on the same physical machine.

For more information about Sun Logical Domains, see the Logical Domains (LDoms) 1.0.3 Administration Guide.