Voting disk and OCR creation

dear all,
Am installing 11gr2 on solaris 10 update 6. We are planning to have ASM also. So I created 3 users
oraasm-ASM OWNER
oracrs-clusterware owner
oracle-oracle database owner.
Now the question is :
Do I have to configure SSH for all the 3 users ?.
Clusterware installaltion should be done by oracrs user and database installation should be done by user ORACLE ?
How to create Voting RAW Disk and CRS RAW DISK ?
I create 2 directories in
bash-3.00$ cd /test/u03/TEST/
bash-3.00$ ls
OCR VOTE
bash-3.00$ dd if=/dev/zero of=/test/u03/TEST/OCR bs=1024 count=100
dd: /test/u03/TEST/OCR: open: Is a directory
Do I have to user root ?
Please advise as am familiar with installation in windows only
Kai

Hi,
Link:[Duplicate thread|http://forums.oracle.com/forums/thread.jspa?threadID=1014776&tstart=0]
Please avoid duplicate thread in multiple categories.
Regards,
X A H E E R

Similar Messages

Why logical partition is a must for voting disk and OCR

Hi Guys,
I just started handling jobs for RAC installation, I have a simple question regarding the setup.
Why does logical partition have to be used for voting disk and OCR?
I tried partition the disk that were provisioned for voting disk and OCR with primary partition but when OUI is trying to recognize the disk, it cannot find the disk that has been partitioned with primary partition.
Thank you,
Adhika

Hello Adhika,
I found it on this doc http://download.oracle.com/docs/cd/B28359_01/install.111/b28250/storage.htm
Be aware of the following restrictions for partitions:
* You cannot use primary partitions for storing Oracle Clusterware files while running the OUI to install Oracle Clusterware as described in Chapter 5, "Installing Oracle Clusterware". You must create logical drives inside extended partitions for the disks to be used by Oracle Clusterware files and Oracle ASM.
* With 32-bit Windows, you cannot create more than four primary disk partitions for each disk. One of the primary partitions can be an extend partition, which can then be subdivided into multiple logical partitions.
* You can assign mount points only to primary partitions and logical drives.
* You must create logical drives inside extended partitions for the disks to be used by Oracle Clusterware files and Oracle ASM.
* Oracle recommends that you limit the number of partitions you create on a single disk to prevent disk contention. Therefore, you may prefer to use extended partitions rather than primary partitions.
For these reasons, you might prefer to use extended partitions for storing Oracle software files and not primary partitions.
All the best,
Rodrigo Mufalani
http://www.mrdba.com.br/mufalani

Voting disk and OCR disk in RAC

Can anyone explain me in basic terms ...
For what Voting and OCR disk are used in RAC.

Hi Francisco,
Thanks for the information.
But i am having lot of doubts in Voting disk and types of heart-beats present in Oracle 10g RAC.
As Oracle says css uses two heart beats 1. Network heart-beat 2. Disk heart-beat
My doubts:
1. How Oracle uses voting disk to avoid split-brain syndrome? OR what is the role of voting disk in split-brain syndrome?
2. How Oracle monitors remote node health?
3. Oracle says there is one more heart-beat where ckpt process keep on writing to control file for every 3 seconds and if it fails lmon process will evict the node....Is it true?
5. Oracle Clusterware will send messages (via a special ping operation) to all nodes configured in the cluster, often called the "heartbeat." If the heartbeat fails for any of the nodes, it checks with the Oracle Clusterware configuration files (Voting disk) to distinguish between a real node failure and a network failure......Is it true? If true then what about the two heart beats(Network and Disk)...why these heart-beats are present or useful?
If possible please clear my doubts by giving some simple examples....
Awaiting for your reply and too much eager to learn and expertise in Oracle RAC architecture before administering it.
Regards,
Yasser.

OCFS2 , ASM and Raw Device for Voting Disk and OCR

Dear all ,
My manager assigned me to establish a 11gRAC , 3 node on OEL. He likes to locate ASM with datafiles , at the same time, 2 OCR vol on OCFS2 and RawDevice respectively , 2 voting disks on OCFS2 and RawDevice respectively also.
This really annoys me .
Oh all experts, could anybody give me some advices ? Can those stuff be co-existed ?

Billy Verreynne wrote:
MccLok wrote:
My manager assigned me to establish a 11gRAC , 3 node on OEL. He likes to locate ASM with datafiles , at the same time, 2 OCR vol on OCFS2 and RawDevice respectively , 2 voting disks on OCFS2 and RawDevice respectively also. Not a great idea to introduce additional s/w layers between the CRS software and its OCR and voting disks. If ocfs2 is for example used as a shared file system for these devices (files), then the ocfs2 cluster s/w needs to be up and running, the shared devices mounted, before CRS can successfully start. Thus any problem with the ocfs2 stack, will impact on CRS. Why? What does ocfs2 buy you in this regard? What are the benefits that justifies the increased complexity and the dependency of CRS on another s/w layer?
Fewer moving parts means less complexity, less stuff that needs to be configured and can go wrong.In fact, some users had perception that " Pay mroe so that Get more".

Backup and Restore OCR,Voting Disk and ASM Disks in new SAN-10g RAC

Dear Friends,
I am using 10g R2 RAC serup on Linux
My OCR,Voting Disk and ASM Disk for DBF Files are on a SAN box
Now i am reorganising SAN by scrapping the entire SAN and cretaing new LUN's (It's a must)
so pleae let me know
1) how do i take backup of OCR and Voting Disk from existing SAN and how do i restore it in new LUN's after SAN reorganisation
2) how do i take backup of existing Database's from existing SAN and how do i restore it in new LUN's after SAN reorganisation.
I will be doing it in Planned downtime only
Regards,
DB

For step 1 you should following metalink doc.
For step 2 here is simple backup command script.
I have done this in windows for you.
D:\app\ranjit\product\11.2.0\dbhome_1\BIN>rman target /
Recovery Manager: Release 11.2.0.1.0 - Production on Wed Feb 8 21:48:47 2012
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
connected to target database: ORCL (DBID=1299593730)
RMAN> run
+{+
allocate channel c1 device type disk format 'D:\app\ranjit\rman\%U';
allocate channel c2 device type disk format 'D:\app\ranjit\rman\%U';
backup database;
backup current controlfile format 'D:\app\ranjit\rman\%U';
+}+
Regards

Confusion with OCFS2 File system for OCR and Voting disk RHEL 5, Oracle11g,

Dear all,
I am in the process of installing Oracle 11g 3 Node RAC database
The environment on which i have to do this implementation is as follows:
Oracle 11g.
Red Hat Linux 5 x86
Oracle Clusterware
ASM
EMC Storage
250 Gb of Storage drive.
SAN
As of now i am in the process of installing Oracle Clusterware on the 3 nodes.
I have performed these tasks for the cluster installs.
1. Configure Kernel Parameters
2. Configure User Limits
3. Modify the /etc/pam.d/login file
4. Configure Operating System Users and Groups for Oracle Clusterware
5. Configure Oracle Clusterware Owner Environment
6. Install CVUQDISK rpm package
7. Configure the Hosts file
8. Verify the Network Setup
9. Configure the SSH on all Cluster Nodes (User Equivalence)
9. Enable the SSH on all Cluster Nodes (User Equivalence)
10. Install Oracle Cluster File System (OCFS2)
11.Verify the Installation of Oracle Cluster File System (OCFS2)
12. Configure the OCFS2 (/etc/ocfs2/cluster.conf)
13. Configure the O2CB Cluster Stack for OCFS2
BUT, here after i am a little bit confused on how to proceed further. The next step is to Format the disk and mount the OCFS2, Create Software Directories... so and so forth.
I asked my system admin to provide me two partitions so that i could format them with OCFS2 file system.
He wrote back to me saying.
*"Is what you want before I do it??*
*/dev/emcpowera1 is 3GB and formatted OCFS2.*
*/dev/emcpowera2 is 3GB and formatted OCFS2.*
*Are those big enough for you? If not, I can re-size and re-format them*
*before I mount them on the servers.*
*the SAN is shared storage. /dev/emcpowera is one of three LUNs on*
*the shared storage, and it's 214GB. Right now there are only two*
*partitions on it- the ones I listed below. I can repartition the LUN any*
*way you want it.*
*Where do you want these mounted at:*
*/dev/emcpowera1*
*/dev/emcpowera2*
*I was thinking if this mounting techique would work like so:*
*emcpowera1: /u01/shared_config/OCR_config*
*emcpowera2: /u01/shared_config/voting_disk*
*Let me know how you'd like them mounted."*
Please recommend me what i should convey to him so that i can ask him to the exact same thing.
My second question is, as we are using ASM, for which i am gonna configure ASM after clusterware installation, should i install Openfiler??
Pls refer the enviroment information i provided above and make recommendations.
As of now i am using Jeffery Hunters guide to install the entire setup. You think the entire install guide goes well with my enviroment??
http://www.oracle.com/technology/pub/articles/hunter_rac11gr1_iscsi.html?rssid=rss_otn_articles
Kind regards
MK

Thanks for ur reply Mufalani,
You have managed to solve half part of my query. But still i am stuck with what kind of mount point i should ask the system admin to create for OCR and Voting disk. Should i go with the mount point he is mentioning??
Let me put forth few more questions here.
1. Is 280 MB ok for OCR and voting disks respectively??
2. Should i ask the system admin to create 4 voting disk mount points and two for ocr??
3. As mentioned by the system admin.
*/u01/shared_config/OCR_config*
*/u01/shared_config/voting_disk*
Is this ok for creating the ocr and voting disks?
4. Can i use OCFS2 file system for formating the disk instead of using them as RAW device!!?
5. As u mentioned that Openfiler is not needed for Configuring ASM... Could you provide me the links which will guide me to create partition disks, voting disks and ocr disks!! I could not locate them on the doc or else were. I did find a couple of them, but was unable to identify a suitable one for my envoirement.
Regards
MK

Why Voting Disk & OCR not on ASM?

What could be the reason not to have Voting disk and OCR on ASM.
Is it that, we require Voting Disk and OCR before ASM? Any idea?

user9198889 wrote:
but this doesnt seem to be a problem with 11.2 anymore! oracle 11g r2 recomends storing ocr and voting disks on asm? why is does?
how does it work ?
i cant get my head around thisOn 11gR2 we can keep OCR and VOTE in ASM Diskgroup.
see start process
http://download.oracle.com/docs/cd/E11882_01/rac.112/e10717/intro.htm#CEGDBFIE
10g -> 11gR1, we create ASM diskgroup from database software
11gR2, we create ASM diskgroup from cluster software.
recomends storing ocr and voting disks on asm? why is does? 11gR2 not support raw devices, support ASM and CFS

Multiplexing Voting Disk in Oracle 11gR2 ??

Dear all,
I have single voting disk residing in data group VDOCRDG with external redundancy. I would like to add two more voting disks to this group. Could you please let me know a way to add 2 more vd's to this disk group or should i create a new disk group with normal redundancy ???
Appreciate if you could provide your answer with SQL commands.
database: oracle 11g r2 patch-1
os: RHEL 5.5
RAC: two-node RAC
ASM: voting disk and OCR reside in ASM
let me know if you need more information.
thanks
P

Just out of curiosity:
(Obviously this is a doc question)
is http://tahiti.oracle.com broken for you, so you must ask others to abstract the documentation for free, or don't you understand the line in the Forums ltiEtiquette Post
reading 'Consulting documentation first is highly recommended'?
I'm getting a bit annoyed by people trying to outsource as much of the task they get paid for to a forum of volunteers.
Sybrand Bakker
Senior Oracle DBA

How can I remove asm and ocr installation in AIX?

Hi,
I try to install single instance with using ASM in AIX.
But I did not make successfully.
Now I want to remove ASM and OCR installation then
I will plan to make new clear installation.
How can I remove asm and ocr ??
Or How can I control my removing is fully correct ?

1) ASM Instance Clean-Up Procedures
Stop all of the databases that use the ASM instance that is running from the Oracle home that is on the node that you are deleting.
On the node that you are deleting, if this is the Oracle home which from which the ASM instance runs, then remove the ASM configuration by completing the following steps. Run the command srvctl stop asm -n node_name for all of the nodes on which this Oracle home exists. Run the command srvctl remove asm -n node for all nodes on which this Oracle home exists. If there are databases on this node that use ASM, then use DBCA Disk Group Management to create an ASM instance on one of the existing Oracle homes on the node, restart the databases if you stopped them.
If you are using a cluster file system for your ASM Oracle home, then ensure that your local node has the $ORACLE_BASE and $ORACLE_HOME environment variables set correctly. Run the following commands from a node other than the node that you are deleting, where node_number is the node number of the node that you are deleting:
rm -r $ORACLE_BASE/admin/+ASMnode_number
rm -f $ORACLE_HOME/dbs/*ASMnode_number
If you are not using a cluster file system for your ASM Oracle home, then run the rm or delete commands mentioned in the previous step on each node on which the Oracle home exists.
2) Deleting an Oracle Clusterware Home Using OUI in Silent Mode
!!! Oracle recommends that you back up your voting disk and OCR files after you complete the node deletion process.
If you ran the Oracle Interface Configuration Tool (OIFCFG) with the -global flag during the installation, then skip this step. Otherwise, from a node that is going to remain in your cluster, from the CRS_home/bin directory, run the following command where node2 is the name of the node that you are deleting:
./oifcfg delif –node node2
Obtain the remote port number, which you will use in the next step, using the following command from the CRS_home/opmn/conf directory:
cat ons.config
From CRS_home/bin on a node that is going to remain in the cluster, run the Oracle Notification Service Utility (RACGONS) as in the following example where remote_port is the ONS remote port number that you obtained in the previous step and node2 is the name of the node that you are deleting:
./racgons remove_config node2:remote_port
On the node to be deleted, run rootdelete.sh as the root user from the CRS_home/install directory. If you are deleting more than one node, then perform this step on all of the other nodes that you are deleting.
From any node that you are not deleting, run the following command from the CRS_home/install directory as the root user where node2,node2-number represents the node and the node number that you want to delete:
./rootdeletenode.sh node2,node2-number
If necessary, identify the node number using the following command on the node that you are deleting:
CRS_home/bin/olsnodes -n
Perform this step only if your are using a non-shared Oracle home. On the node or nodes to be deleted, run the following command from the CRS_home/oui/bin directory where node_to_be_deleted is the name of the node that you are deleting:
./runInstaller -updateNodeList ORACLE_HOME=CRS_home
"CLUSTER_NODES={node_to_be_deleted}"
CRS=TRUE -local
Deinstall the Oracle Clusterware home from the node that you are deleting using OUI as follows by running the following command from the Oracle_home/oui/bin directory, where CRS_home is the name defined for the Oracle Clusterware home:
./runInstaller -deinstall –silent "REMOVE_HOMES={CRS_home}"
Perform step 9 from the previous section about using OUI interactively under the heading "Deleting an Oracle Clusterware Home Using OUI in Interactive Mode".

Only ONE voting disk created on EXTERNAL redundancy

Hi All,
I am wondering why, when configuring 5 LUNs, then creating one DG with these 5 LUNS...
then creating OCR/Vote disk , GRID installer only creates one voting disk?
Of course, I can always create another voting disk in a separate DG...
any ideas>?
of course, when I try " ocrconfig -add +OCR_DG" i get a message that says OCR is already configured....
thanks

Hi JCGO,
you are mixing up voting disks and OCR.
Voting disks are placed on the disk header of an ASM diskgroup. The number of voting disks is based on the redundancy of the diskgroup:
External (no mirroring) = 1; Normal = 3; High redundancy (triple mirroring) = 5;
The OCR however is saved as a normal file (like any datafile of a tablespace) inside ASM and therefore "inherits" the redundancy of the diskgroup.
So while you only see 1 file, the blocks of the file are mirrored correspondingly (either double or triple (High)).
Voting disks can only reside in one diskgroup. You cannot create another voting disk in a separate DG. And the command to add voting disks ist:
crsctl add votediskHowever this won't work when on ASM, you can only replace them into another DG:
crsctl replace votedisk +DGThe OCR on the other side, since a normal file, allows additional OCRs to be created in different diskgroups.
Since it is the heart of the cluster (and also containing backups of the voting disks) it does make sense to "logically" mirror it additionally (even if it already is based on the mirroring of the DG). Since if the DG cannot be mounted maybe another one containing actual OCR can. This is a little better than using the OCR backup (which can be up to to 4 hours old).
Hence in my cluster installation I always put the OCR in every diskgroup I have (up to a number of 5).
And since my clusters normally have 3 diskgroups (1 OCRVOT, 1 DATA and 1 FRA), I end up with 3.
Having an uneven number of OCR is a little superior over having an even number (so 3 or 5 vs. 2 or 4). I skip the explanation to why.
Regards
Sebastian

How do I define 2 disk groups for ocr and voting disks at the oracle grid infrastructure installation window

Hello,
It may sound too easy to someone but I need to ask it anyway.
I am in the middle of building Oracle RAC 11.2.0.3 on Linux. I have 2 storage and I created three LUNs in each of storage so 6 LUNs in total look in both of servers. If I choose NORMAL as a redundancy level, is it right to choose my 6 disks those are created for OCR_VOTE at the grid installation? Or should I choose only 3 of them and configure mirroring at latter stage?
The reason why I am asking this is that I didn't find any place to create asm disk group for ocr and voting disks at the oracle grid infrastructure installation window. In fact, I would to like to create two disk groups in which one of groups contains three disks those were brought from storage 1 and the second one contains rest three 3 disk that come from the last storage.
I believe that you will understand the manner and help me on choosing proper way.
Thank you.

Hi,
You have 2 Storage H/W.
You will need to configure a Quorum ASMDisk to store a Voting Disk.
Because if you lose 1/2 or more of all of your voting disks, then nodes get evicted from the cluster, or nodes kick themselves out of the cluster.
You must have the odd number of voting disk (i.e 1,3 or 5) one voting disk per ASM DISK, So 1 Storage will hold more voting disk than another storage.
(e.g 3 Voting Disk - 2 voting stored in stg-A and 1 voting disk store in stg-B)
If fail the storage that hold the major number of Voting disk the whole cluster (all nodes) goes down. Does not matter if you have a other storage online.
It will happen:
https://forums.oracle.com/message/9681811#9681811
You must configure your Clusterware same as RAC extended
Check this link:
http://www.oracle.com/technetwork/database/clusterware/overview/grid-infra-thirdvoteonnfs-131158.pdf
Explaining: How to store OCR, Voting disks and ASM SPFILE on ASM Diskgroup (RAC or RAC Extended) | Levi Pereira | Oracl…

OCR and Voting Disk Migration to new media

Hello,
We need to move OCR,voting disk and ASM from one storage media to another .I think ASM related files are very easy to move/re map but how OCR and Voting Disk files will be migrated to the new storage media?
Thanks,
S.Mann

Hi,
when you said:
"Move Voting Disk : run as root.
crsctl query css votedisk
crsctl add css votedisk new_backup_san_device
crsctl query css votedisk - Make sure the new device is added
crsctl delete css votedisk current_san_device_to_be_encrypted
crsctl query css votedisk - Make sure that the old one is removed "
I supose the new_backup_san_device could be a raw device??
In my system I have a 2 nodes cluster, oracle 10gR2, RAC and ASM
the ocr and voting disk are stored in /dev/raw/raw1 and /dev/raw/raw2
thoses 2 raw devices are mapped with LUNS in the first storade media.
We are about to change it..
So what must I do at this step? What are the logical steps I must done?
add the new LUNS in the nodes and map it as raw devices?
I have this at the moment:
crw-r----- 1 root oinstall 162, 1 Feb 8 17:33 /dev/raw/raw1
crw-r----- 1 root oinstall 162, 2 Feb 8 17:33 /dev/raw/raw2
crw-r----- 1 oracle oinstall 162, 3 Feb 8 17:33 /dev/raw/raw3
in the case of migration, I must add 3 new row devices?
as this?
crw-r----- 1 root oinstall 162, 1 Feb 8 17:33 /dev/raw/raw1
crw-r----- 1 root oinstall 162, 2 Feb 8 17:33 /dev/raw/raw2
crw-r----- 1 oracle oinstall 162, 3 Feb 8 17:33 /dev/raw/raw3
crw-r----- 1 root oinstall 162, 1 Feb 8 17:33 /dev/raw/raw4
crw-r----- 1 root oinstall 162, 2 Feb 8 17:33 /dev/raw/raw5
crw-r----- 1 oracle oinstall 162, 3 Feb 8 17:33 /dev/raw/raw6
That's it?
Thanks to help

Defining OCR / Voting disks

I followed this guide
http://www.oracle-base.com/articles/11g/OracleDB11gR2RACInstallationOnOEL5UsingVMwareServer2.php#install_grid_infrastructure
to install "clusterware" on my SLES11 maschines.
Question:
In 10g I were able to select which disks a for voting and which are for ocr.
Does it make sense to create different ASM Diskgroups for OCR and Voting, and where can I select which diskgroup should be used ?

zekeriya, you are only right for Version 10. Things changed with Oracle 11. Now you cannot store vote and ocr on raw devices, only in ASM or a cluster filesystem. I know it is a chicken-and-egg problem and I have not quite understood how they do it but that's how things work now.
You can store voting disks and the OCR on Oracle Automatic Storage Management (Oracle ASM), or a certified cluster file system.See this link for more details
http://download.oracle.com/docs/cd/E11882_01/rac.112/e10717/votocr.htm#CHDJDFIC
And yes, it'd recommend to use a special diskgroup just for these.
Bjoern

Regarding Voting disk recovery scenarios

Hi,
For years i have read about RAC and Voting disk and it is said that each node should access more than half of the voting disks but never got a chance to work on the below scnerios which i have mentioned, if some one has practical done the below scenarios or have good knowledge do let me know.
1) If i have 5 voting disks and out of which 2 got corrupted or deleted will the cluster keep working properly? If i boot my system or restart the cluster will it still work fine or not?
2) The above scenario with 3 voting disk deleted or got corrupted what will happen?
3) If i have 2 OCR and i got deleted or corrupted will the system run fine?

Aman,
During startup the clusterware requires the majority of votes to start the CSS Daemon.
The majority is counted on how many was configured, not how many remain alive.
Below test using 3 Votedisk (11.2.0.3)
alert.log
[cssd(26233)]CRS-1705:Found 1 configured voting files but 2 voting files are required, terminating to ensure data integrity; details at (:CSSN                     M00021:) in /u01/app/11.2.0/grid/log/node11g02/cssd/ocssd.log
ocssd.log
2014-11-14 05:20:05.126: [    CSSD][3021551360]clssnmvDiskVerify: Successful discovery of 1 disks
2014-11-14 05:20:05.126: [    CSSD][3021551360]clssnmCompleteInitVFDiscovery: Completing initial voting file discovery
2014-11-14 05:20:05.126: [    CSSD][3021551360]clssnmCompleteVFDiscovery: Completing voting file discovery
2014-11-14 05:20:05.126: [    CSSD][3021551360]clssnmvDiskStateChange: state from discovered to pending disk /dev/asm-ocr-vote01
2014-11-14 05:20:05.126: [    CSSD][3021551360]clssnmvDiskStateChange: state from pending to configured disk /dev/asm-ocr-vote01
2014-11-14 05:20:05.126: [    CSSD][3021551360]clssnmvVerifyCommittedConfigVFs: Insufficient voting files found, found 1 of 3 configured, needed 2 voting files
With 2 voting files online, no problem, clusterware start with warning on logs.
Ps. If was configured a diskgroup (OCR_VOTE) with high redundancy (5 asmdisk each in your onw failgroup), even diskgroup can hold 3 asmdisk failure. The diskgroup goes down and if there is only one OCR (no mirror) on that Diskgroup the whole clusterware goes down.

Minimum number of voting disks?

Hi,
Is there is a minimum number of voting disks?
does that depend on the RAC nodes?
If I have 4 nodes what is the optimal voting disks?
Thanks

user9202785 wrote:
Hi,
Is there is a minimum number of voting disks?
does that depend on the RAC nodes?
If I have 4 nodes what is the optimal voting disks?
ThanksOracle recommends 3 voting disk. but you can install clusterware with one voting disk by selecting external redudancy during clusterware installation.
the number of voting disks is not depend on the number of RAC nodes. you can have upto maximum 32 voting disks for 2nodes to 100 RAC nodes.
The Oracle Clusterware is comprised primarily of two components: the voting disk and the OCR (Oracle Cluster Registry). The voting disk is nothing but a file that contains and manages information of all the node memberships and the OCR is a file that manages the cluster and RAC configuration.
refer : how to add/remove/repace voting disk in the below link:
http://oracleinstance.blogspot.com/2009/12/how-to-addremovereplacemove-oracle.html.
if voting disk fails: refer
http://oracleinstance.blogspot.com/2009/12/how-to-addremovereplacemove-oracle.html.
also refer Oracle® Database 2 Day + Real Application Clusters Guide 10g Release 2 (10.2)
read the below ,hope this will help you.
1) Why do we have to create odd number of voting disk?
As far as voting disks are concerned, a node must be able to access strictly more than half of the voting disks at any time. So if you want to be able to tolerate a failure of n voting disks, you must have at least 2n+1 configured. (n=1 means 3 voting disks). You can configure up to 32 voting disks, providing protection against 15 simultaneous disk failures.
Oracle recommends that customers use 3 or more voting disks in Oracle RAC 10g Release 2. Note: For best availability, the 3 voting files should be physically separate disks. It is recommended to use an odd number as 4 disks will not be any more highly available than 3 disks, 1/2 of 3 is 1.5...rounded to 2, 1/2 of 4 is 2, once we lose 2 disks, our cluster will fail with both 4 voting disks or 3 voting disks.
2) Does the cluster actually check for the vote count before node eviction? If yes, could you expain this process briefly?
Yes. If you lose half or more of all of your voting disks, then nodes get evicted from the cluster, or nodes kick themselves out of the cluster.
3) What's the logic behind the documentaion note that says that "each node should be able to see more than half of the voting disks at any time"?
The answer to first question itself will provide answer to this question too.answered by: Boochi
refer: Question on voting disk
Question on voting disk

Voting disk and OCR creation

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