Configuration Guidelines for RAID-1 Volumes

• Before you create a mirror, create the RAID-0 (stripe or concatenation) volumes that comprise the mirror.

• When creating a mirror, first create a one-way mirror, then attach a second submirror. This strategy starts a resynchronization operation. This strategy also ensures that data is not corrupted. You can also create a one-way mirror for use as a future two-way or multi-way mirror.

• You can create a two-way mirror, three-way mirror, or four-way mirror from a one-way mirror with a single command. You can speed the creation process by creating all submirrors with a single command. Use this process only if you are not mirroring existing data and if you are comfortable destroying the data on all of the submirrors.

• You can create a RAID-1 volume from an existing file system that is built on a slice. Only the single slice may be included in the primary RAID-0 volume (submirror). If you are mirroring root or other system-critical file systems, all submirrors must consist of only a single slice.

• Use the swap -l command to check for all swap devices. Each slice that is specified as swap must be mirrored independently from the remaining swap slices.

• The Enhanced Storage tool within the Solaris Management Console does not support unmirroring root (/), /opt, /usr, or swap. In fact, the tool does not support unmirroring any file system that cannot be unmounted while the system is running. Instead, use the command-line procedure for these file systems.

• Use submirrors of the same size. Submirrors of different sizes result in unused disk space.

• Use only similarly configured submirrors within a mirror. In particular, if you create a mirror with an unlabeled submirror, you cannot attach any submirrors that contain disk labels.

• You can 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 in this situation, the following error message displays:

  can't attach labeled submirror to an unlabeled mirror

  Either all submirrors intended for use within a specific mirror must start on cylinder 0, or all of the submirrors must not start on cylinder 0.

  Starting cylinders do not have to be the same across all submirrors. However, all submirrors must either include or not include cylinder 0.

• You can improve a mirror's performance by adding additional state database replicas before you create the mirror. As a general rule, add two additional replicas for each mirror you add to the system. Solaris Volume Manager uses these additional replicas to store the dirty region log (DRL), which is used to provide optimized resynchronization. By providing adequate numbers of replicas, you can minimize I/O impact on RAID-1 volume performance. Using at least two replicas on the same disks or controllers as the mirror that the replicas log also helps to improve overall performance.

• Only mount the mirror device directly. Do not try to mount a submirror directly, unless the submirror is offline and mounted read-only. Do not mount a slice that is part of a submirror. This process could destroy data and crash the system.