Who is joining the cluster? Who is leaving the cluster? To determine periodically whether all members are alive, a voting mechanism is used to check the validity of each member. All members in the database group vote by providing details of what they presume the instance membership bitmap looks like andthe bitmap is stored in the GRD Global Resource Directory.
A predetermined master member tallies the vote flags of the status flag and communicates to the respective processes that the voting is done; then it waits for registration by all the members who have received the reconfigured bitmap.
CKPT writes into a single block that is unique for each instance, thus intra-instance coordination is not required. This block is called the checkpoint progress record. All members attempt to obtain a lock on a control file record the result record for updating. The instance that obtains the lock tallies the votes from all members.
The control file vote result record is stored in the same block as the heartbeat in the control file checkpoint progress record.
There will be some situation where the leftover write operations from failed database instances The cluster function failed on the nodes, but the nodes are still running at OS level reach the storage system after the recovery process starts. Since these write operations are no longer in the proper serial order, they can damage the consistency of the data stored data.
Therefore when a cluster node fails, the failed node needs to be fenced off from all the shared disk devices or disk groups. Voting disk Files is used by CSS to determine which nodes are currently members of the cluster. In concert with other Cluster components such as CRS to shut down, fence, or reboot either single or multiple nodes whenever network communication is lost between any nodes within the cluster, in order to prevent the dreaded split-brain condition in which two or more instances attempt to control the RAC database.
It thus protects the database information. Voting disk will be used by the CSS daemon to arbitrate with peers that it cannot see over the private interconnect in the event of an outage, allowing it to salvage the largest fully connected sub cluster for further operation.
It checks the voting disk to determine if there is a failure on any other nodes in the cluster. During this operation, NM Node Monitor will make an entry in the voting disk to inform its vote on availability. Similar operations are performed by other instances in the cluster.
The three voting disks configured also provide a method to determine who in the cluster should survive. For example, if eviction of one of the nodes is necessitated by an unresponsive action, then the node that has two voting disks will start evicting the other node. NM Node Monitor alternates its action between the heartbeat and the voting disk to determine the availability of other nodes in the cluster. There are few different scenarios possible with missing heart beats: Network heart beat is successful, but disk heart beat is missed.
Disk heart beat is successful, but network heart beat is missed. Both heart beats failed. Few possible scenarios: Nodes have split in to N sets of nodes, communicating within the set, but not with members in other set.
Just one node is unhealthy. By default Misscount is less than Disktimeout seconds. Also, if there is a vendor clusterware in play, then misscount is set to The following are the default values in seconds for the misscount parameter and their respective versions when using Oracle Clusterware: Operating System RAC Oracle 10g R1 and R2 Oracle 11g R1 and R2 Windows 30 30 Linux 60 30 Unix 30 30 VMS 30 30 Below given table will also provide you the different possibilities of individual heartbeat failures on the basis of misscount.
A split-brain occurs when cluster nodes hang or node interconnects fail, and as a result, the nodes lose the communication link between them and the cluster. Split-brain is a problem in any clustered environment and is a symptom of clustering solutions and not RAC. Split-brain conditions can cause database corruption when nodes become uncoordinated in their access to the shared data files.
For a two-node cluster, split-brain occurs when nodes in a cluster cannot talk to each other the internode links fail and each node assumes it is the only surviving member of the cluster.
To prevent data corruption, one node must be asked to leave the cluster or should be forced out immediately. If a vendor clusterware is used, split-brain resolution is left to it and Oracle would have to wait for the clusterware to provide a consistent view of the cluster and resolve the split-brain issue.
This can potentially cause a delay and a hang in the whole cluster because each node can potentially think it is the master and try to own all the shared resources. Still, Oracle relies on the clusterware for resolving these challenging issues. You are commenting using your Google account. You are commenting using your Twitter account.
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Thanks Like Like. Bruce Like Like. Very nice! Operations on the voting disk must be run as root. Up to version 11gR2 after any addition or removal of a node in the cluster a backup of the RV must be done. Without any of these, your entire cluster will stop working.
During the process of installing and configuring the Grid Infrastructure, we have the option to choose only one disk-group to store the Clusterware information. The process to recover each one is different, so if we can simplify it means that we will have a faster recovery, therefore less downtime. So that we can separate them into distinct diskgroups we will initially have OCR and VD in a single diskgroup , since we have no other option during Grid Infrastructure installation.
Figure 4 — Define a name and location to store your disk. Figure 5 — Repeat the same process for the other disks. Create vd2. Repeat the procedure for all other newly created disks: ocr2. Figure 9 — After changing the disks, add them to the other node of your cluster.
Figure 12 — Repeat the procedure for the other disks: vd2. Start only one of the nodes , because we will partition them and then configure them in ASM. The command listed all disks present on the node. The older RAC release called a voting disk a quorum disk, but today it is all called a voting disk.
In essence, a voting disk determine which RAC nodes are members of a cluster. Nodes instances can be "evicted" and there is always one "master" node that controls other nodes. For high availability, Oracle recommends that you have a minimum of three voting disks. The RAC heartbeat is a polling mechanism that is sent over the cluster interconnect to ensure that all RAC nodes are available.
ASM in 11gR2 and beyond chooses a couple of blocks at predefined positions of every disk for the voting disk information.
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