Solaris Volume Manager Administration Guide

Background Information for Defining State Database Replicas

In general, it is best to distribute state database replicas across slices, drives, and controllers, to avoid single points-of-failure. You want a majority of replicas to survive a single component failure. If you lose a replica (for example, due to a device failure), it might cause problems with running Solaris Volume Manager or when rebooting the system. Solaris Volume Manager requires at least half of the replicas to be available to run, but a majority (half plus one) to reboot into multiuser mode.

When you work with state database replicas, consider the following Recommendations for State Database Replicas and Guidelines for State Database Replicas.

Recommendations for State Database Replicas

You should create state database replicas on a dedicated slice of at least 4 Mbytes per replica. If necessary, you could create state database replicas on a slice that will be used as part of a RAID 0, RAID 1, or RAID 5 volume, soft partitions, or transactional (master or log) volumes. You must create the replicas before you add the slice to the volume. Solaris Volume Manager reserves the starting part of the slice for the state database replica.
You can create state database replicas on slices that are not in use.
You cannot create state database replicas on existing file systems, or the root (/), /usr, and swap file systems. If necessary, you can create a new slice (provided a slice name is available) by allocating space from swap and then put state database replicas on that new slice.
A minimum of 3 state database replicas are recommended, up to a maximum of 50 replicas per Solaris Volume Manager disk set. The following guidelines are recommended:
- For a system with only a single drive: put all three replicas in one slice.
- For a system with two to four drives: put two replicas on each drive.
- For a system with five or more drives: put one replica on each drive.
If you have a RAID 1 volume that will be used for small-sized random I/O (as in for a database), be sure that you have at least two extra replicas per RAID 1 volume on slices (and preferably disks and controllers)that are unconnected to the RAID 1 volume for best performance.

Guidelines for State Database Replicas

You can add additional state database replicas to the system at any time. The additional state database replicas help ensure Solaris Volume Manager availability.

Caution –
If you upgraded from Solstice DiskSuite^TM to Solaris Volume Manager and you have state database replicas sharing slices with file systems or logical volumes (as opposed to on separate slices), do not delete the existing replicas and replace them with new replicas in the same location.

The default state database replica size in Solaris Volume Manager is 8192 blocks, while the default size in Solstice DiskSuite was 1034 blocks. If you delete a default-sized state database replica from Solstice DiskSuite, then add a new default-sized replica with Solaris Volume Manager, you will overwrite the first 7158 blocks of any file system that occupies the rest of the shared slice, thus destroying the data.
When a state database replica is placed on a slice that becomes part of a volume, the capacity of the volume is reduced by the space that is occupied by the replica(s). The space used by a replica is rounded up to the next cylinder boundary and this space is skipped by the volume.
By default, the size of a state database replica is 4 Mbytes or 8192 disk blocks. Because your disk slices might not be that small, you might want to resize a slice to hold the state database replica. For information about resizing a slice, see “Administering Disks (Tasks)” in System Administration Guide: Basic Administration.
If multiple controllers exist, replicas should be distributed as evenly as possible across all controllers. This strategy provides redundancy in case a controller fails and also helps balance the load. If multiple disks exist on a controller, at least two of the disks on each controller should store a replica.