Planning Volume Management

This section provides the following guidelines for planning volume management of your cluster configuration:

• Guidelines for Volume-Manager Software

• Guidelines for Solaris Volume Manager Software

• File-System Logging

• Mirroring Guidelines

Oracle Solaris Cluster software uses volume-manager software to group disks into device groups which can then be administered as one unit. Oracle Solaris Cluster software supports Solaris Volume Manager software You must install Solaris Volume Manager software on all voting nodes of the cluster.

See your volume-manager documentation and Configuring Solaris Volume Manager Software for instructions about how to install and configure the volume-manager software. For more information about the use of volume management in a cluster configuration, see Multihost Devices in Oracle Solaris Cluster Concepts Guide and Device Groups in Oracle Solaris Cluster Concepts Guide.

Guidelines for Volume-Manager Software

Consider the following general guidelines when you configure your disks with volume-manager software:

• Software RAID – Oracle Solaris Cluster software does not support software RAID 5.

• Mirrored multihost disks – You must mirror all multihost disks across disk expansion units. See Guidelines for Mirroring Multihost Disks for guidelines on mirroring multihost disks. You do not need to use software mirroring if the storage device provides hardware RAID as well as redundant paths to devices.

• Mirrored root – Mirroring the root disk ensures high availability, but such mirroring is not required. See Mirroring Guidelines for guidelines about deciding whether to mirror the root disk.

• Unique naming – You might have local Solaris Volume Manager volumes that are used as devices on which the /global/.devices/node@nodeid file systems are mounted. If so, the name of each local volume on which a /global/.devices/node@nodeid file system is to be mounted must be unique throughout the cluster.

• Node lists – To ensure high availability of a device group, make its node lists of potential masters and its failback policy identical to any associated resource group. Or, if a scalable resource group uses more nodes than its associated device group, make the scalable resource group's node list a superset of the device group's node list. See the resource group planning information in the Oracle Solaris Cluster Data Services Planning and Administration Guide for information about node lists.

• Multihost disks – You must connect, or port, all devices that are used to construct a device group to all of the nodes that are configured in the node list for that device group. Solaris Volume Manager software can automatically check for this connection at the time that devices are added to a disk set.

• Hot-spare disks – You can use hot-spare disks to increase availability, but hot spare disks are not required.

See your volume-manager documentation for disk layout recommendations and any additional restrictions.

Guidelines for Solaris Volume Manager Software

Consider the following points when you plan Solaris Volume Manager configurations:

• Local volume names – The name of each local Solaris Volume Manager volume on which a global-devices file system, /global/.devices/node@nodeid, is mounted must be unique throughout the cluster. Also, the name cannot be the same as any device-ID name.

• Dual-string mediators – A disk string consists of a disk enclosure, its physical disks, cables from the enclosure to the host or hosts, and the interface adapter cards. Each disk set configured with exactly two disk strings and mastered by exactly two Oracle Solaris hosts is called a dual-string disk set. Such a disk set must have Solaris Volume Manager dual-string mediators configured. Observe the following rules when you configure dual-string mediators:

  • You must configure each disk set with two or three hosts that act as mediator hosts.

  • You must use the hosts that can master a disk set as mediators for that disk set. If you have a campus cluster, you can also configure a third node or a non-clustered host on the cluster network as a third mediator host to improve availability.

  • Mediators cannot be configured for disk sets that do not meet the two-string and two-host requirements.

  See the mediator(7D) man page for details.

File-System Logging

Logging is required for UFS cluster file systems. Oracle Solaris Cluster software supports Oracle Solaris UFS logging. See the mount_ufs(1M) man page for more information.

Solaris Volume Manager supports both types of file-system logging.

Mirroring Guidelines

This section provides the following guidelines for planning the mirroring of your cluster configuration:

• Guidelines for Mirroring Multihost Disks

• Guidelines for Mirroring the Root Disk

Guidelines for Mirroring Multihost Disks

To mirror all multihost disks in an Oracle Solaris Cluster configuration enables the configuration to tolerate single-device failures. Oracle Solaris Cluster software requires that you mirror all multihost disks across expansion units. You do not need to use software mirroring if the storage device provides hardware RAID as well as redundant paths to devices.

Consider the following points when you mirror multihost disks:

• Separate disk expansion units – Each submirror of a given mirror should reside in a different multihost expansion unit.

• Disk space – Mirroring doubles the amount of necessary disk space.

• Three-way mirroring – Solaris Volume Manager software supports three-way mirroring. However, Oracle Solaris Cluster software requires only two-way mirroring.

• Differing device sizes – If you mirror to a device of a different size, your mirror capacity is limited to the size of the smallest submirror.

For more information about multihost disks, see Multihost Devices in Oracle Solaris Cluster Concepts Guide.

Guidelines for Mirroring the Root Disk

For maximum availability, mirror root (/), /usr, /var, /opt, and swap on the local disks. However, Oracle Solaris Cluster software does not require that you mirror the root disk.

Before you decide whether to mirror the root disk, consider the risks, complexity, cost, and service time for the various alternatives that concern the root disk. No single mirroring strategy works for all configurations. You might want to consider your local Oracle service representative's preferred solution when you decide whether to mirror root.

See your volume-manager documentation and Configuring Solaris Volume Manager Software for instructions about how to mirror the root disk.

Consider the following points when you decide whether to mirror the root disk.

• Boot disk – You can set up the mirror to be a bootable root disk. You can then boot from the mirror if the primary boot disk fails.

• Complexity – To mirror the root disk adds complexity to system administration. To mirror the root disk also complicates booting in single-user mode.

• Backups – Regardless of whether you mirror the root disk, you also should perform regular backups of root. Mirroring alone does not protect against administrative errors. Only a backup plan enables you to restore files that have been accidentally altered or deleted.

• Quorum devices – Do not use a disk that was configured as a quorum device to mirror a root disk.

• Quorum – Under Solaris Volume Manager software, in failure scenarios in which state database quorum is lost, you cannot reboot the system until maintenance is performed. See your Solaris Volume Manager documentation for information about the state database and state database replicas.

• Separate controllers – Highest availability includes mirroring the root disk on a separate controller.

• Secondary root disk – With a mirrored root disk, the primary root disk can fail but work can continue on the secondary (mirror) root disk. Later, the primary root disk might return to service, for example, after a power cycle or transient I/O errors. Subsequent boots are then performed by using the primary root disk that is specified for the eeprom(1M) boot-device parameter. In this situation, no manual repair task occurs, but the drive starts working well enough to boot. With Solaris Volume Manager software, a resync does occur. A resync requires a manual step when the drive is returned to service.

  If changes were made to any files on the secondary (mirror) root disk, they would not be reflected on the primary root disk during boot time. This condition would cause a stale submirror. For example, changes to the /etc/system file would be lost. With Solaris Volume Manager software, some administrative commands might have changed the /etc/system file while the primary root disk was out of service.

  The boot program does not check whether the system is booting from a mirror or from an underlying physical device. The mirroring becomes active partway through the boot process, after the volumes are loaded. Before this point, the system is therefore vulnerable to stale submirror problems.