Mirror and Submirror Requirements and Guidelines

When you are working with RAID-1 volumes (mirrors) and RAID-0 volumes (single-slice concatenations), consider the following guidelines.

Custom JumpStart and Solaris Live Upgrade Guidelines

The custom JumpStart installation method and Solaris Live Upgrade support a subset of the features that are available in the Solaris Volume Manager software. When you create mirrored file systems with these installation programs, consider the following guidelines.

• The term RAID-0 volume can refer to disk stripes or disk concatenations. The custom JumpStart and Solaris Live Upgrade installation methods only enable you to create single-slice concatenations. You cannot create RAID-0 stripe volumes during the installation or upgrade.

• The custom JumpStart installation method enables you to create up to two submirrors for each mirror. The Solaris Live Upgrade installation method enables you to create up to three submirrors for each mirror. Two submirrors usually provide sufficient data redundancy for most applications, and the disk drive costs are less expensive. Three submirrors enable you to take a submirror offline and perform a backup while maintaining the two remaining submirrors for continued data redundancy.

• If you create mirrored file systems with the custom JumpStart installation method, you do not need to create the file systems that you are mirroring before you create the mirror.

Guidelines for Selecting Disks and Controllers

When you choose the disks and controllers that you want to use to mirror a file system, consider the following guidelines.

• Use components that are on different controllers to increase the number of simultaneous reads and writes that can be performed.

• Keep the slices of different submirrors on different disks and controllers. Data protection is diminished considerably if slices of two or more submirrors of the same mirror are on the same disk.

• Organize submirrors across separate controllers, because controllers and associated cables tend to fail more often than disks. This practice also improves mirror performance.

• Use the same type of disks and controllers in a single mirror. Particularly in old SCSI storage devices, different models or brands of disk or controller can have widely varying performance. Mixing the different performance levels in a single mirror can cause performance to degrade significantly.

Guidelines for Selecting Slices

When you choose the slices that you want to use to mirror a file system, consider the following guidelines.

• Any file system, including root (/), swap, and /usr, can use a mirror. Any application, such as a database, also can use a mirror.

• Make sure that your submirror slices are of equal size. Submirrors of different sizes result in unused disk space.

• If you have a mirrored file system in which the first submirror attached does not start on cylinder 0, all additional submirrors you attach must also not start on cylinder 0. If you attempt to attach a submirror starting on cylinder 0 to a mirror in which the original submirror does not start on cylinder 0, the following error message is displayed:

  can't attach labeled submirror to an unlabeled mirror

  You must ensure that all submirrors you plan to attach to a mirror either all start on cylinder 0, or that none of them start on cylinder 0.

  Starting cylinders do not have to be identical across all submirrors, but all submirrors must either include or not include cylinder 0.