Quorom disks on EVA5000

[JPS-LTU]

Hi there,

can anyone explain how quorom disks (im talking about EVA quorom disks here - not cluster quorom disks) work, and what affect removing disk groups on the eva may have on them

Cheers
jason

[Steven Clementi · Accepted solution]

Jason:

Are you sure you have the right terminology?

I have never heard of anything on an EVA be referred to as "quorum" and I have been installing them since VCS1.x


Steven

[Ivan Ferreira]

I'm working with EVA, BC and CA, and I never heard about the term quorum.

[Sameer_Nirmal]

Initially , the default disk group will have 5 quorum disks which holds EVA metadata.

When a new DG is created, one quorum disk is created on it and one quorum ( vote ) disk is removed from the default DG.
So every DG will have one quorum disk and one can maximum 16 such disks as DG max is 16 on EVA 5000.

When a DG is removed , its quorum ( vote ) disk is returned back to default DG.

[Steven Clementi]

Sameer:

Do you have a document or a link to a document that explains this? I knew about "quorum"'s on other types of Arrays like Hitachi, EMC, etc, but was unaware that the EVA employed such a system as well.

What does this "quorum" do? Does it reside in the metadata portion of the disk? or take up physical space?


Steven

[Mario_66]

Hi,

guys, I have to say that you are very lucky if you have never heard about EVA qourum disks :).

I do not think that it is important to know how quorum disks work (EVA takes care about that), but it is important to know that you should have at least 5 of them on the working storage system. Max. number is 16. If for some reason you have a problem it is better to call support then make a wrong choice.

Let's assume that you have two disk groups. The most probably your EVA will have 4 Q disks in one group and 1 Q disk in the second disk group. If you need to remove the second disk group then one of the disks in the first DG will become Q disk. Again you have 5 of them.

Regards,
Mario.

[Steven Clementi]

Mario:

I understand the part about how they move back and forth as you create/delete Disk Groups, but what other purpose does it serve on the EVA? What is it "voting" for?

Potentially, I can see it voting internal to the DG on things like... Which 6 disk RSS set gets the next disk to be added to the group... but globally?


Steven

[Mario_66]

Hi,

quorum disks hold some controler information.

E.g. WWN, storage system name, character map of disk groups and virtual disk members, etc.

Controller somehow has to find out on which disk subsystem is going to connect to, what is there and check that everything is OK.

Regards,
M.

[Ivan Ferreira]

Ohhhhh!, now I remember:

System-level metadata is stored on quorum disks and contains:
- Controller information
- WWN and storage system name
- Character map of disk groups and virtual disk members

When a storage system is created, there are five quorum disks in the default disk
group. There is always a maximum of 16 quorum disks (one per disk group).

When a new disk group is created:

O- ne quorum disk is created on it.
- One quorum disk is removed from the default disk group until just one quorum disk remains.
- Metadata overhead is +/- 0.2% of total disk group capacity.

I can't beleave it how i forgot about this. I had to re-read the documentation.

[Steven Clementi]

I always just considered it metadata, so just another name for what I already knew.

First time I heard it referred to as "quorum" so I guess I did learn someting new today.


Steven

[JPS-LTU]

Thanks for all the replies guys...

all very well explained :)
now i know what im talking about!

Jason