diff --git a/Documentation/faq.md b/Documentation/faq.md index 0f72f9d0f..cb50e7cb2 100644 --- a/Documentation/faq.md +++ b/Documentation/faq.md @@ -72,7 +72,7 @@ etcdctl provides a `snapshot` command to create backups. See [backup][backup] fo When replacing an etcd node, it's important to remove the member first and then add its replacement. -etcd employs distributed consensus based on a quorum model; (n+1)/2 members, a majority, must agree on a proposal before it can be committed to the cluster. These proposals include key-value updates and membership changes. This model totally avoids any possibility of split brain inconsistency. The downside is permanent quorum loss is catastrophic. +etcd employs distributed consensus based on a quorum model; (n/2)+1 members, a majority, must agree on a proposal before it can be committed to the cluster. These proposals include key-value updates and membership changes. This model totally avoids any possibility of split brain inconsistency. The downside is permanent quorum loss is catastrophic. How this applies to membership: If a 3-member cluster has 1 downed member, it can still make forward progress because the quorum is 2 and 2 members are still live. However, adding a new member to a 3-member cluster will increase the quorum to 3 because 3 votes are required for a majority of 4 members. Since the quorum increased, this extra member buys nothing in terms of fault tolerance; the cluster is still one node failure away from being unrecoverable.