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.fredi...@upx.com <mailto:fernando.fredi...@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/
_______________________________________________
Users mailing list
Users@ovirt.org
http://lists.ovirt.org/mailman/listinfo/users
