Questions about fibres and Quorum

[alexia32]

Hello

How can we check if the fiber adapter is a 1Gb or 2gb etc.. via command line?

Quorum needs to be activate on cluster env? If we need to change the value can it be done online?

Thanks in advance

Cheers
Al

 

[khalidaaa]

For your first question (how to know the fiber adapter speed), use the fcstat command:

http://publib.boulder.ibm.com/infoc...pic=/com.ibm.aix.cmds/doc/aixcmds2/fcstat.htm

fcstat fcsX | grep Port Speed

Where X is your fiber channel number.

For the second, have a look at this link:

http://publib.boulder.ibm.com/infoc...hacmp.geolvm/ha_glvm_quorum_forced_varyon.htm

It is recommended to disable quorum on HACMP clusters and IMHO you can't enable/disbale online!

Regards,
Khalid

 

[sjm2]

Khalid said: "It is recommended to disable quorum on HACMP clusters". Who recommended it? Where is that documented? Because as far as I know that is not always true. Note that what we mean by "quorum" in a PowerHA (pka HACMP) cluster is actually AIX LVM quorum checking.

 

[khalidaaa]

Sorry, i was refering to HACMP/XD for GLVM:

In general, it is recommended to disable quorum for geographically mirrored volume groups in order to minimize the possibility of leaving the resource group in the ERROR state. In HACMP, quorum loss for a volume group causes HACMP to selectively move the affected resource group to another node. Similarly, in HACMP/XD for GLVM, if quorum is enabled and then lost for a geographically mirrored volume group, HACMP may start a selective fallover event (logged in hacmp.out as an rg_move for the resource group).

Regards,
Khalid

 

[alexia32]

Hi

Thanks a lot for the fcstat command I didn't know this one!

About the Quorum I am still very confused! I have found this also from IBM and still don;t know if I need to have the quorum disable or enable???

IBM said:
Setting up quorum correctly when laying out a volume group is very important.
Quorum must be enabled on concurrent volume groups.
With quorum enabled, a two-disk non-concurrent volume group puts you at risk for losing quorum and data access.
The failure of a single adapter or cable would cause half the disks to be inaccessible. HACMP provides some protections to avoid the failure, but planning is still important.


=> So that means for concurrent volume group (example Oracle RAC VG) should have the quorum enable

and also does this means that any vg on SAN disks should have quorum enable (non concurrent vg, hacmp vg or non hacmp vg)???

Very confused ...

Thanks in advance for your help

Cheers
Al

 

[khalidaaa]

If you are planning to mirror your data at the AIX level to provide redundancy, you will need to consider AIX quorum checking on a volume group. If you aren't mirroring your data at the AIX level (like SAN's LUN mirroring), quorum isn't an issue.

When a quorum is lost, the volume group varies itself off so that the disks are no longer accessible by the Logical Volume Manager (LVM). This prevents further disk I/O to that volume group so that data is not lost or assumed to be written when physical problems occur. Additionally, as a result of the vary off, the user is notified in the error log that a hardware error has occurred and service must be performed. 

This has implications when you want to use disk mirroring in order to ensure high availability. In a two disk mirrored system, if the first disk fails, then you have lost 66 percent of your VGDAs, and the entire volume group becomes unavailable. This defeats the purpose of mirroring. For this reason, three or more (and generally an odd number) disk units provide a higher degree of availability and are highly recommended where mirroring is desired.

http://web.utanet.at/mario/exam/5129c62.htm

Regards,
Khalid

 

[khalidaaa]

Taken from HACMP course manual:

HACMP 4.5 and up automatically reatcs to a "loss of quorum" (LVM_SA_QUORCLOSE) error associated with a vg going offline on a cluster. In response to this error, a non-concurrent resource group goes offline on the node where the error occured. If the AIX 5L LVM takes a vg in the resource group offline due to a loss of quorum for the vg on the node, HACMP selectively moves the resource group to another node.

You can change this default behavior by customizing resource recovery to use a notify method instead of fallover.

I'm still looking why its not the case for concurrent rgs!

Regards,
Khalid

 

[sjm2]

Khaled that is taken from a very old HACMP course manual ... been a while since 4.5

 

[khalidaaa]

sjm2, no it isn't! That "loss of quorum" message was being handled since that version of HACMP!

Regards,
Khalid

 

[alexia32]

Hello

Sorry guys for the delay.
I have found the answer from IBM documentation after searching!
So Concurrent volume group has to have Quorum enable!
I made the change.

Thanks again for your help.

cheers
Al