Split-brain Syndrome

Similar Questions

• Who decides the surviving node during the detection of split brain?

  How oracle decides which node be deported upon detection of split brain when all nodes have written in the voting record, but unable to check the heart rate through interconnection.

  Ajay

  Hi Ajay,

  the complexity of this depends on the amount of nodes in the cluster and how is isolated (and how), but generally speaking "the cluster creates an invisible group (cohorts) between nodes, which could potentially cause corruption and should be resolved. » Oracle Clusterware manages the "split brain" scenario in putting an end to all nodes in the smallest cohort. "If the cohorts are the same size, the cohort with the smallest number node inside survives." (Cited in Apress - Expert Oracle RAC diagnostic Performance and Tuning by Murali vandenberghe)

  Best regards

  Stefan Koehler

  Researcher and consultant independent of Oracle performance

  Twitter: @OracleSK

• OCR and voting disk

  Hi all
  
  What is the difference b/w OCR and voting disk

  The voting disk is a file that manages information about the node membership and OCR is a file that manages the cluster and RAC database configuration information.

  Vote of disc - Oracle Clusterware uses the drive to vote to determine which instances are members of a cluster. The voting disk must reside on a shared disk. Basically, all the nodes of the RAC cluster register their heartbeat information on teas voting records. The number will determine the number of nodes in the RAC cluster. They are also used to check availability of instances at the JRC and remove the unavailable out of the cluster nodes. It helps prevent the condition "split brain" and maintains intact the database information. The split brain syndrome and its effects and how it has been successful in oracle is mentioned below.
  For high availability, Oracle recommends to have a minimum of three disks with voting rights. If you configure a single voting disk, then you must use external mirror to provide redundancy. You can have up to 32 disks with right to vote in your cluster. What I could understand the odd value of the number of disks to vote is that a Noah should see voting disk to continue to operate, so with 2 maximum number, if he sees that 1, is not the maximum value but one half of the value of the voting disk. I always try to look for more on this concept.

  OCR (Oracle Cluster registry) - is located on the shared storage, and maintains information on the configuration of the cluster and cluster database. OCR contains such information which instances of database nodes and services that is running on what database.

  Registry of Cluster Oracle (OCR) is such a component in 10g THAT CARS used to store the cluster configuration information. It is a component of shared disk, usually placed in a shared gross volume that must be accessible to all nodes in the cluster. The demon OCSSd manages the configuration information in the OCR and maintains the changes in the cluster registry.

  ocrcheck is the command to check the OCR.

• Why do we file or drive to vote vote

  Hi all
  
  What is the need to vote folder or disk? I know that he has the information n node all the. But if the nodes can ping all other nodes what is the need of the voting disk.
  
  Can you please explain.
  
  
  PS: I read the
  
  Oracle® database
  Clusterware Oracle and Oracle Real Application Clusters
  Deployment and administration guide
  10g Release 2 (10.2)
  
  But could not find how much it actually come into picture.
  
  Thank you in anticipation

  For example, a node 2 RAC - instance 'A' and 'B' instance

  Lets assume that the bodies A & B instance is unable to communicate with each other. Now, this could be of the fact that the other instance is really down or because there is a problem with the communication of the interconnection between the instances.

  A "split brain" occurs when bodies are unable to talk with others due to problem of communication of interconnection and each instance can think that it is the only case of survivor and start the update of the database. It is obviously problematic, isn't it?

  To avoid half a brain, two bodies are required to update the drive to vote regularly.

  Now consider the earlier judgment of the perspecive of one of the nodes:

  case 1) instance B is actually down:-here, looking for the instance of A perspective; There is no communication on the interconnection with the instance B and also instance B is not to update the voting disk ('coz he is down). Instance A can assume that the instance B is low and it can go in providing services and update the database.

  Case 2) the problem is with interconnection communication:-here, looking for the instance of A perspective; There is no communication on the interconnection with the B instance. However we can see this instance B is updating the drive to vote; which means instance B is not really down. This State is true view of the B instance; We can see that instance A updates the drive to vote but may not speak of A Forum on the interconnection. At this point, both rush and try to lock the drive to vote, and who gets the lock eject the other, thus avoiding "Split Brain" syndrome.

  It is the underlying theory using a voting drive.

  When instances of a RAC boot, one of the instances will be assigned the master. In the case of a "split brain" the captain Gets the lock on the drive to vote and survives. In reality the instance with the number of the lower node remains, even if the problem is with the map of internetwork on this node :)

  See you soon.

• What css will do if some of the votedisk failed?  and why

  4 lymph Oracle 10 g RAC 2 with 5 disks, what happens if 5 votedisk $N get failed?
  
  $N = 2, zero impact?
  $N = 3?
  $N = 4?
  
  and what is the reason.
  
  Thanks in advance.
  
  Published by: shahand on December 1st, 2008 17:59

  shahand, I suggest you to read carefully the day 2 rac guide as the Rac administration guide.

  you're talking about these concepts are well discussed and exlpained in very simple terms (no need to buy other books before I read the official documentatio available for free)

  But back to our business and your question:

  The voting disk saves the node membership information.
  A node must be able to access more than half the disks with right to vote at any time.
  For example, if you have five voting disks configured, then a node must be able to access at least three drives with right to vote at any time.

  If a node cannot access the required minimum number of discs with right to vote, it is expelled or removed from the cluster.

  This avoids the split brain syndrome.

• How to avoid the brain while using external redundancy.

  Hi all

  When Oracle creates disk to vote who is in external redundancy he writes only in a single drive even if we provide 3 disks for the disk group. In this scenario, what will happen during the expulsion of node. Is there a scenario of split brain.

  Ajay

  Ajay Vijayan wrote:

  I would like to know more about it. How do the multiple vote available in external redundancy disk?

  You can not. If you want three voice files, use a group configured for normal redundancy.

• Add new N3048 to current stack of switch

  Hello

  I have a new N3048 switch to add to our current stack of 2 N3048 to provide more capacity. Before lighting for the first time, that I would like to know if I need to run through the initial configuration or can I just connect the new battery switch and power, it will then get the config of the switch?

  The firmware must also update on the battery, can I do this first or when all 3 switches are in the stack?

  Thank you very much.

  Since the existing battery and the new, we can have different firmware revisions, generally the best route is updating the firmware on the existing stack, and then on the new switch to add before attaching it to the battery. You should not need to do any initial configuration before attaching. As always recommended is to use a ring topology when stacking to avoid "split brain" IP address and duplicate problems are common with chain failures.

  B

• Loss of links FI L1/L2

  Hello

  One of my customers wonder about linking the FI 2 L1/L2 loss.

  In my mind, this case should not be here, why we have 2 links but I don't know what happened exactly in this case... the 2 FI become master of the UCS cluster...

  any idea or already Tester?

  THX

  The L1/L2 are by data management engine (DME) to synchronize the config only - there is no path of data on these links.

  In case these links both go down, there is a rear mechanism built into the system to prevent split brain.  Each frame has a SEEPROM (flash).  Within the SEEPROM, there is a shared area each FI can read & write to and two subzones; an inmate by each FI in which only FI can write to.  The subareas are used to store information about the config DB fails to a bank owner in the same, changes are made and it is reintroduced.  You will avoid 'stale' config overwrite any changes made during a FI was disconnected.

  If there is a failure in the cluster llink (L1/L2), IF read and write small counters in the shared area.  This serves as a secondary heartbeat to warn the other FI is always active.  Meanwhile, the cluster starts in a State of 'Failed-Link' and prevents any election primary/secondary.  Everything else as-if - primary primary, secondary rest is secondary.

  Kind regards

  Robert

• You can cluster consistency of data centers?

  We currently lack two separate groups of coherence in the different data centers. One is prod the other DR.

  Would it not possible for nodes in each cluster to create a cluster that spans two data centers? Then in a failover scenario data would be available.

  I know that pulse of nodes of coherence between them to keep the members of the classes and there is a TTL parameter to determine the life of package. Would have nodes in data centres resulting in pulses being missed or TTLs killing packages?

  Did anyone had success with this?

  Performance of coherence is related to the latency between the nodes. Having a single distributed cluster on 2 data centers might harm performance (some wait times might have to be changed to prevent the nodes from A data center to claim another node in datacenter B is out of scope/possibly dead).

  When you lose the network connectivity between 2 data centers (note I do not say "If you lose connectivity". This WILL happen), you are welcome in the 'world of split brain', each half of the grid to believe the other is dead and who claim to be the 'master '. And so if you have a replicated data on N nodes, master backups are sent back in each data center, performance for a few minutes (the time of course depends on many parameters...). And of course the data will no longer be synchronized between 2 data centers. The quorum must be thought out and stuff like that...

  I could be wrong, but as far as I know I'd rather have 2 separate groups. I think 12.1 has new features to replicate the data the main grid to the Dominican Republic one, I was not through any new documentation.

• Deployment

  I wonder if anyone can help

  We are a hosting provider and we have two data center related to 10 Gbit/s dark fiber that is very resistant are the data center about six kilometers

  Would it be possible to deploy an analytic node at each site with a being the main and the other one (on another site) being the ha node. We have one vlan stretched between the data center

  I saw some documents indicating that analytical nodes must be in the same data center with not more than 5 ms latency with our dark fiber, however we can easily accommodate this

  Thanks in advance for your help

  The analytic nodes should be on the same vlan in one place not only because of the latency, but also because the very bad things that can happen to your cluster in a split brain scenario. VROPS HA does not handle brain, and in function of how long it has split you could have a lot of difficulty doing online in one piece. When you sit down and you really think that the use case through, stretching from the cluster will not give you anything above that keep the cluster at the same place. I would say that play it safe, to make what is supported and keep them in the same ms.

• Oracle RAC 11 g fencing

  Hi all, I want to know if anyone knows the process of closing on the CARS, the other question is, Oracle RAC is able to restart the nodes (physical servers)?

  Thank you very much.

  Pablo

  The Oracle Clusterware is designed to perform a node eviction by removing one or more nodes in the cluster if a critical problem is detected.  A critical problem could be a node does not not by a heartbeat of network, a node does not by a heartbeat of disc, a machine hooked or severely degraded, deprivation of resources OS (IE high use of the processor, memory shortage/Swapping, queue/executed load medium high) or an ocssd.bin process hanging.

  For example,.

  Oracle Clusterware is based on the files of voting accessibility. If a node in the cluster cannot access the majority of the files of voting, the node (s) to which it applies is (are)

  immediately removed from the cluster (expelled / closed).

  This expulsion of node is intended to maintain the overall health of the cluster by removing members wrong (in other words, in order to avoid "split brain" situations, as well as data corruption).

  Note: From 11.2.0.2 RAC (or if you're on Exadata), expulsion of node may not actually reboot the machine.  It's what we call a restart without rebooting.  In this case, we reboot most of the clusterware battery to see if that solves the unhealthy node.

  For more information on 11 g RAC 2: REBOOT - LESS NŒUD FENCING, refer to the following URL:

  URL: http://oracleinaction.com/11g-r2-rac-reboot-less-node-fencing/

• Get Machine plans associated with objects of a Service catalog

  In our vCAC, we have a service with the catalog items that vSphere available machines virtual via cloning model. In a vCO script, is there a way to get objects of schema associated with each point objects catalog in our service? If so, can you provide the code to show how it's done? We have vCAC 6.1 and vCO 5.5.2.Thanks!

  OK, I finally found the answer courtesy of Automation vRA (vCAC) using vRO - Split Brain :

  «Each element of the catalog has an attribute of providerBinding.» This package contains the bindingId value. This link ID is the ID of the master plan (virtualMachineTemplateID) of the part of IaaS. That's how vRA figures on what course of action to deploy when you request a catalogue point. »

  So, given an vCACCAFECatalogItem object, I can get the ID of associated like this blueprint:

  var blueprintId = catalogItem.getProviderBinding () .getBindingId ();

• Nodes political foreclosure

  Hi all
  I have a problem on a stretched production cluster, running node 2 RAC Oracle 11 GR 2 located in two different sites.

  The problem we face is, node 1 of the cluster on site 1 lost the external connectivity on both private and public interconnections.

  In this case, nodes 1 and 2 have the network heartbeat check on the private interconnect, but node 2 still have public interconnection where many applications are working.

  According to the Oracle political ouster, at this point, the master node (perhaps the node with the smallest number of node) sends a signal "kill" on the other node to avoid a potential effect "Split Brain".

  I was wondering, is there any polocy that I put up just to set a priority among the nodes? I want to preserve "alive" of the accessible node by applications (node2 with public interconnection just straight up) and let the other node (node 1 with the two connections down) should be deported.

  I'd appreciate your answers really.

  Hello

  There is no way in which you can give priority to a node in order to always be a master node. Algorithms possible one where a node can be defined as a master node are as follows

  -The node that began first in the cluster

  -The node that remained up during a maintenance activity where, in the other node would have been worn down

  How you can identify a master node is

  -Watching the crsd newspaper and checking nodes newspaper later 'I AM THE NEW MASTER of the OCR' or 'NEW OCR MASTER IS.

  -ocrconfig - showbackup (the node that owns and hosts the last backup of the ocr

  Kind regards

  Vautrin - Oracle

• Ethernet link e MacAddress Duplicato

  Salve a tutti,

  Ho una Centos5 con interfaccie 2 ethernet in collage.

  Since it liaison crea one ' con interfaccia macaddress uguale a quello di una delle due schede di rete, Vmware Workstation e tell error macaddress duplicato di mi part di network TR blocca.

  Esiste UN some workaround by risolvere he problema?

  Grazie a tutti

  Ciao

  Antonio

  MI sono guardato song questo documento.

  http://pbraun.nethence.com/doc/SysUtils/MCSG.html

  e vedo che viene of the binding of the he usato by pulsation of the rete di, m'immagino dato che debba essere ridondata per evitare di "split brain" me del cluster (TR of di avere O infatti due O una subnet subnet con collage).

  SEI sicuro che non vada anche con una semplice scheda di rete, o al massimo assegnando due schede single? In a VMware ridondanza delle connessioni viene garantita dai portgroup e ambiente vswitch given dedicated che nel invited.

  Ciao,.

  Luca.

• Failback puts the servers as passive

  Hi, I got the following from a customer scenario and I was wondering if it was the expected configuration or if there is a misconfiguration in which what is ancient:

  Once a failover occurs because of the failure of (public and channel interface) network connectivity, it shifts on the passive server as expected.  But once the former principal server takes over the access to the network, both servers are marked as liabilities so it shuts down the services Heartbeat and manual intervention is required for the installation configuration.

  This behavior is expected or y at - there some configuration problem for restoration?

  Yes, it's a default behavior. Otherwise when the network connection is handed over to two virtual machines protected by heartbeat, the two will try to be active together and you will see a split brain scenerio. It's normal, administrator will need to manually decide which is the only one to be active, start and perform the synchronization of the passive later.