This section provides the following guidelines for planning the mirroring of your cluster configuration:
Mirroring 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 or plex 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 or plex.
For more information about multihost disks, see Multihost Devices in Oracle Solaris Cluster Concepts Guide .
Oracle Solaris ZFS is the default root file system in the Oracle Soalris release. See How to Configure a Mirrored Root Pool (SPARC or x86/VTOC) in Managing ZFS File Systems in Oracle Solaris 11.2 for instructions about how to mirror the ZFS root pool. Also see Chapter 4, Managing ZFS Root Pool Components, in Managing ZFS File Systems in Oracle Solaris 11.2 for information about how to manage the different root pool components.
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 ZFS root pool.
Consider the following points when you decide whether to mirror the ZFS root pool:
Boot disk – You can set up the mirror to be a bootable root pool. You can then boot from the mirror if the primary boot disk fails.
Backups – Regardless of whether you mirror the root pool, 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 pool.
Separate controllers – Highest availability includes mirroring the root pool on a separate controller.