在12.1.2.3.0中，引入了Quorum Disk Manager这个功能。以1/8为例，存储节点有3个，OCR存储的磁盘组创建为Normal，voting disk有3个，这时如果其中两个存储节点出现故障（voting disk只有1个），这时你的集群就挂了。为了解决这个问题，出现了这个功能。还以1/8为例，存储节点有3个，OCR存储的磁盘组创建为HIGH（3个来自存储节点，2个来自计算节点），这时voting disk有5个，这时如果两个存储节点出现故障，voting disk还有3个，还可以保证集群正常运行。这个功能通过计算节点上的IB口通过iSCSI来实现。
crsctl query css votedisk
## STATE File Universal Id File Name Disk group
-- ----- ----------------- --------- --------- 1. ONLINE ca2f1b57873f4ff4bf1dfb78824f2912 (o/192.168.10.41/DATAC1_CD_09_celadm01) [SYSTEMDG] 2. ONLINE a8c3609a3dd44f53bf17c89429c6ebe6 (o/192.168.10.42/DATAC1_CD_09_celadm02) [SYSTEMDG] 3. ONLINE cafb7e95a5be4f00bf10bc094469cad9 (o/192.168.10.43/DATAC1_CD_09_celadm03) [SYSTEMDG] 4. ONLINE 4dca8fb7bd594f6ebf8321ac23e53434 (/dev/exadata_quorum/QD_SYSTEMDG_DB01) [SYSTEMDG] 5. ONLINE 4948b73db0514f47bf94ee53b98fdb51 (/dev/exadata_quorum/QD_SYSTEMDG_DB02) [SYSTEMDG] Located 5 voting disk(s).
官方的解释
The Quorum Disk Manager utility, introduced in Oracle Exadata release 12.1.2.3.0, helps you to manage the quorum disks.
The utility enables you to create an iSCSI quorum disk on two of the database nodes and store a voting file on those two quorum disks. These two additional voting files are used to meet the minimum requirement of five voting files for a high redundancy disk group. This feature is only applicable to Oracle Exadata racks that meet the following requirements:
The Oracle Exadata rack has fewer than five storage servers.
The Oracle Exadata rack has at least two database nodes.
The Oracle Exadata rack has at least one high redundancy disk group.
The feature allows for the voting files to be stored in a high redundancy disk group on Oracle Exadata racks with fewer than five storage servers due to the presence of two extra failure groups.
Without this feature, voting files are stored in a normal redundancy disk group on Exadata racks with fewer than five storage servers. This makes Oracle Grid Infrastructure vulnerable to a double partner storage server failure that results in the loss of the voting file quorum, in turn resulting in a complete cluster and database outage. Refer to My Oracle Support note 1339373.1 for restarting the clusterware and databases in this scenario.
The iSCSI quorum disk implementation has high availability because the IP addresses on ib0 and ib1 are highly available using RDS. The multipathing feature ensures the iSCSI quorum disk implementation will work seamlessly if a more flexible or isolated internal network configuration is implemented in the future.
Each iSCSI device shown in the figure below corresponds to a particular path to the iSCSI target. Each path corresponds to an InfiniBand port on the database node. For each multipath quorum disk device in an active–active system, there are two iSCSI devices, one for ib0 and the other for ib1.
查看quorum disk的信息
/opt/oracle.SupportTools/quorumdiskmgr --list --config
/opt/oracle.SupportTools/quorumdiskmgr --list --target
Reference
http://docs.oracle.com/cd/E80920_01/DBMMN/maintaining-exadata-database-servers.htm#DBMMN22868
