Re: RAC vote 11gR2 Question
- From: "Radoulov, Dimitre" <cichomitiko@xxxxxxxxx>
- To: smishra_97@xxxxxxxxx, "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 27 Sep 2013 10:36:46 +0200
Hi Sanjay,
On 27/09/2013 00:42, Sanjay Mishra wrote:
> 1. If I had OCR/Voting Disk in ASM diskgroup with Normal Redundancy and three
> Disk defined in ASM Diskgroup creation are from three different SAN. Now
> question is that where is the OCR primary and Mirror created in this case. I
> was reading somewhere on one site and it mentioned that there is only one
> copy of OCR on one diskgroup and so in order for protection and best
> practices, second OCR has to tbe second diskgroup. Can someone correct as
> what is correct architecture.
Quoting the documentation:
Oracle® Grid Infrastructure Installation Guide 11g Release 2 (11.2) for
Linux
For Oracle Clusterware files, Normal redundancy disk groups provide 3
voting disk files, 1 OCR and 2 copies
(one primary and one secondary mirror). With normal redundancy, the
cluster can survive the loss of one failure group.
In other words:
RAC and Oracle Clusterware Best Practices and Starter Kit (Platform
Independent) (Doc ID 810394.1)
For those who wish to utilize Oracle supplied redundancy for the OCR and
Voting Disks in 11gR2 and above one could create a separate (3rd) ASM
Diskgroup having a minimum of 3 fail groups (total of 3 disks). This
configuration will provide 3 Voting Disks (1 on each fail group) and a
single OCR which takes on the redundancy of that disk group (mirrored
within ASM).
The minimum size of the 3 disks that make up this normal redundancy
diskgroup is 1GB.
Regarding an OCR copy to a separate diskgroup, Oracle® Clusterware
Administration and Deployment Guide
11g Release 2 (11.2) states:
If OCR is stored in an Oracle ASM disk group with _external redundancy_,
then Oracle recommends that you add another OCR location to another disk
group to avoid the loss of OCR, if a disk fails in the disk group.
But the best practice document on MOS - RACGuides_Rac11gR2OnLinux.pdf -
describes the following implementation:
- normal redundancy asm dg for OCR and voting
- ocr mirror on a separate asm dg
And says:
It is Oracle's Best Practice to have an OCR mirror stored in a second
diskgroup. To follow this
recommendation add an OCR mirror. Mind that you can only have one OCR in
a diskgroup.
> 2. On my site, I saw OCRVOTE diskgroup with the following kind of syntax.
> Please ignore the syntax
> create diskgroup ocrvote
> failuregroup 1 disk
> orcl:1
> orcl:2
> orcl:3
> orcl:4
> failuregroup 2 disk
> orcl:5
> orcl:6
> orcl:7
> orcl:8
> failuregroup 3 disk
> orcl:9
> orcl:10
> orcl:11
> orcl:12
>
> So it has used 12 disk where 1-4 are from One SAN and 5-6 from Second and
> 9-12 from third one. Now this is done so as to avoid the Voting disk
> availability and so any one SAN failure will not cause eviction. Question is
> why or what is advantage of using 12 disks here. Isn't it a wastage of 9
> disks here as three disks can provide the same availability
No, it doesn't provide the same availability: with the above
configuration you can loose up to three disks per failure group.
Note that if you loose a controller/FG your cluster _should_ remain up
(i.e. you'll have at least one node running),
but you may(actually "will") still have some nodes evicted.
Regards
Dimitre
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