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Solaris Volume Manager Administration Guide
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Document Information


1.  Getting Started With Solaris Volume Manager

2.  Storage Management Concepts

3.  Solaris Volume Manager Overview

4.  Solaris Volume Manager for Sun Cluster (Overview)

5.  Configuring and Using Solaris Volume Manager (Scenario)

6.  State Database (Overview)

About the Solaris Volume Manager State Database and Replicas

Understanding the Majority Consensus Algorithm

Administering State Database Replicas

Handling State Database Replica Errors

Scenario--State Database Replicas

7.  State Database (Tasks)

8.  RAID-0 (Stripe and Concatenation) Volumes (Overview)

9.  RAID-0 (Stripe and Concatenation) Volumes (Tasks)

10.  RAID-1 (Mirror) Volumes (Overview)

11.  RAID-1 (Mirror) Volumes (Tasks)

12.  Soft Partitions (Overview)

13.  Soft Partitions (Tasks)

14.  RAID-5 Volumes (Overview)

15.  RAID-5 Volumes (Tasks)

16.  Hot Spare Pools (Overview)

17.  Hot Spare Pools (Tasks)

18.  Disk Sets (Overview)

19.  Disk Sets (Tasks)

20.  Maintaining Solaris Volume Manager (Tasks)

21.  Best Practices for Solaris Volume Manager

22.  Top-Down Volume Creation (Overview)

23.  Top-Down Volume Creation (Tasks)

24.  Monitoring and Error Reporting (Tasks)

25.  Troubleshooting Solaris Volume Manager (Tasks)

A.  Important Solaris Volume Manager Files

B.  Solaris Volume Manager Quick Reference

C.  Solaris Volume Manager CIM/WBEM API


Understanding the Majority Consensus Algorithm

An inherent problem with replicated databases is that it can be difficult to determine which database has valid and correct data. To solve this problem, Solaris Volume Manager uses a majority consensus algorithm. This algorithm requires that a majority of the database replicas agree with each other before any of them are declared valid. This algorithm requires the presence of at least three initial replicas, which you create. A consensus can then be reached as long as at least two of the three replicas are available. If only one replica exists and the system crashes, it is possible that all volume configuration data will be lost.

To protect data, Solaris Volume Manager does not function unless half of all state database replicas are available. The algorithm, therefore, ensures against corrupt data.

The majority consensus algorithm provides the following:

If insufficient state database replicas are available, you must boot into single-user mode and delete enough of the corrupted or missing replicas to achieve a quorum. See How to Recover From Insufficient State Database Replicas.

Note - When the total number of state database replicas is an odd number, Solaris Volume Manager computes the majority by dividing the number in half, rounding down to the nearest integer, then adding 1 (one). For example, on a system with seven replicas, the majority would be four (seven divided by two is three and one-half, rounded down is three, plus one is four).