Hi all,
Since I have worked with version 11.2 I had a concept about Quorum Failgroup and its purpose, now reading the documentation 12c I'm confuse about some aspect and want your views on this subject.
My Concept About Quorum Failgroup:
The Quorum Failgroup was introduced in 11.2 for setup with Extended RAC and/or for setup with Diskgroups that have only 2 ASMDISK using Normal redundancy or 3 ASMDISK using High redundancy.
But if we are not using Extended RAC and/or have a Diskgroup Normal Redundancy with 3 or more ASMDISK or Diskgroup High Redundancy with 5 or more ASMDISK the use of Quorum Failgroup is optional, most like not used.
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Documentation isn't clear about WHEN we must to use Quorum Failgroup.
https://docs.oracle.com/database/121/CWLIN/storage.htm#CWLIN287
7.4.1 Configuring Storage for Oracle Automatic Storage Management
2. Choose the Oracle ASM redundancy level to use for the Oracle ASM disk group.
Except when using external redundancy, Oracle ASM mirrors all Oracle Clusterware files in separate failure groups within a disk group. A quorum failure group, a special type of failure group, contains mirror copies of voting files when voting files are stored in normal or high redundancy disk groups. If the voting files are in a disk group, then the disk groups that contain Oracle Clusterware files (OCR and voting files) have a higher minimum number of failure groups than other disk groups because the voting files are stored in quorum failure groups.
A quorum failure group is a special type of failure group that is used to store the Oracle Clusterware voting files. The quorum failure group is used to ensure that a quorum of the specified failure groups are available. When Oracle ASM mounts a disk group that contains Oracle Clusterware files, the quorum failure group is used to determine if the disk group can be mounted in the event of the loss of one or more failure groups. Disks in the quorum failure group do not contain user data, therefore a quorum failure group is not considered when determining redundancy requirements in respect to storing user data.
As mentioned in documentation above, I could understand that in ANY diskgroup that use Normal or High Redundancy MUST have a Quorum failgroup. (does not matter what setup)
In my view, if a Quorum Failgroup is used to ENSURE that a quorum of the specified failure groups are available, then we must use it, in other words is mandatory.
What's your view on this matter?
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Another Issue:
Suppose the following scenario (example using NORMAL Redundancy).
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Example 1
- Diskgroup Normal Redundancy with 3 ASMDIKS.
DSK_0000 - FG1 (QUORUM FAILGROUP)
DSK_0001 - FG2 (REGULAR FAILGROUP)
DSK_0002 - FG3 (REGULAR FAILGROUP)
The ASM will allow create only one Quorum Failgroup, and two Regular Failgroup ( a failgroup to each asm disk)
Storing Votedisk on this diskgroup the all three asmdisk will be used one votedisk in each asm disk.
Storing OCR on this diskgroup the two Regular Failgroup will be used, only one OCR and primary extents and mirror of its extents accross two failgroup. (quorum failgroup will not be used to OCR)
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Example 2
- Diskgroup Normal Redundancy with 5 ASMDIKS.
DSK_0000 - FG1 (REGULAR FAILGROUP)
DSK_0001 - FG2 (REGULAR FAILGROUP)
DSK_0002 - FG3 (QUORUM FAILGROUP)
DSK_0003 - FG4 (QUORUM FAILGROUP)
DSK_0004 - FG5 (QUORUM FAILGROUP)
The ASM will allow create up to three Quorum Failgroup, and two Regular Failgroup.
Storing Votedisk on this diskgroup the all three QUORUM FAILGROUP will be used. REGULAR FAILGROUP will not be used.
Storing OCR on this diskgroup the two Regular Failgroup will be used, only one OCR and primary extents and mirror of its extents accross two failgroup. (none quorum failgroup will not be used to OCR).
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This right here below is confuse to me.
https://docs.oracle.com/database/121/CWLIN/storage.htm#CWLIN287
7.4.1 Configuring Storage for Oracle Automatic Storage Management
2. Choose the Oracle ASM redundancy level to use for the Oracle ASM disk group.
The quorum failure group is used to determine if the disk group can be mounted in the event of the loss of one or more failure groups.
- Normal redundancy: For Oracle Clusterware files, a normal redundancy disk group requires a minimum of three disk devices (two of the three disks are used by failure groups and all three disks are used by the quorum failure group) and provides three voting files and one OCR and mirror of the OCR. When using a normal redundancy disk group, the cluster can survive the loss of one failure group.For most installations, Oracle recommends that you select normal redundancy disk groups.
- High redundancy: For Oracle Clusterware files, a high redundancy disk group requires a minimum of five disk devices (three of the five disks are used by failure groups and all five disks are used by the quorum failure group) and provides five voting files and one OCR and two mirrors of the OCR. With high redundancy, the cluster can survive the loss of two failure groups.
Documentation says:
minimum of three disk devices: two of the three disks are used by failure groups and all three disks are used by the quorum failure group for normal redundancy.
minimum of five disk devices: three of the five disks are used by failure groups and all five disks are used by the quorum failure group for high redudancy.
Questions :
What this USED mean?
How the all disk are USED by quorum failgroup?
This USED mean used to determine if the disk group can be mounted?
How Quorum Failgroup determine if a diskgroup can be mounted, what is the math?
Consider following scenery:
Diskgroup Normal Redundancy with 3 ASM Disks. (Two Regular failgroup and One Quorum Failgroup)
If we lost the Quorum failgroup group. We can mount that diskgroup using force option.
If we lost one Regular failgroup group. We can mount that diskgroup using force option.
We can't lost two Failgroup at same time.
If I don't use Quorum failgroup (i.e only Regular Failgroup) the result of test is the same.
I see no difference between use Quorum Failgroup and only Regular Failgroup on this matter.
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When Oracle docs says:
- one OCR and mirror of the OCR for normal redundancy
- one OCR and two mirrors of the OCR for high redundancy
What this means is we have ONLY ONE OCR File and mirror of its extents, but oracle in documentation says 1 mirror of OCR (normal redundancy) and 2 mirror of OCR (high redudancy).
What is sound like? a single file or two or more files ?
Please don't confuse it with ocrconfig mirror location.