[ovirt-users] Hyperconverged Setup and Gluster healing

[Denis Chaplygin]

With arbiter volume you still have a replica 3 volume, meaning that you
have three participants in your quorum. But only two of those participants
keep the actual data. Third one, the arbiter, stores only some metadata,
not the files content, so data is not replicated 3 times.

On Mon, Apr 24, 2017 at 3:33 PM, FERNANDO FREDIANI <
fernando.frediani at upx.com> wrote:

> But then quorum doesn't replicate data 3 times, does it ?
>
> Fernando
>
> On 24/04/2017 10:24, Denis Chaplygin wrote:
>
> Hello!
>
> On Mon, Apr 24, 2017 at 3:02 PM, FERNANDO FREDIANI <
> fernando.frediani at upx.com> wrote:
>
>> Out of curiosity, why do you and people in general use more replica 3
>> than replica 2 ?
>>
>
> The answer is simple - quorum. With just two participants you don't know
> what to do, when your peer is unreachable. When you have three
> participants, you are able to establish a majority. In that case, when two
> partiticipants are able to communicate, they now, that lesser part of
> cluster knows, that it should not accept any changes.
>
>
>> If I understand correctly this seems overkill and waste of storage as 2
>> copies of data (replica 2)  seems pretty reasonable similar to RAID 1 and
>> still in the worst case the data can be replicated after a fail. I see that
>> replica 3 helps more on performance at the cost of space.
>>
>> You are absolutely right. You need two copies of data to provide data
> redundancy and you need three (or more) members in cluster to provide
> distinguishable majority. Therefore we have arbiter volumes, thus solving
> that issue [1].
>
> [1] https://gluster.readthedocs.io/en/latest/Administrator%
> 20Guide/arbiter-volumes-and-quorum/
>
>
>
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