Minimal number of nodes for production

Tom Zeng tom at
Wed Apr 10 18:02:30 EDT 2013

Thanks Eric for the info, that's very helpful.  7 was mentioned at the last
Riak DC meetup. not as the minimal but for better performance, when I was
chatting with a couple of Basho devs about performance benchmarking, and
about Riak is quite a bit slower on single node against Mongo.

On Wed, Apr 10, 2013 at 5:56 PM, Eric Redmond <eredmond at> wrote:

> On Apr 10, 2013, at 2:26 PM, Tom Zeng <tom at> wrote:
> Hi list,
> We have a production installation with only 3 nodes and running on 1.2.1.
>  I'd appreciate to get some  facts to convince IT to increase the number of
> nodes to 7 and upgrade to 1.3.  I heard people from Basho mentioned ideally
> 7 nodes for production a couple of time, can someone explain why 7, is 4,
> or 5 nodes good enough?
> I'm not sure where you heard the number 7 as a minimum, unless if was for
> a specific use-case. In general the minimum recommended number is 5 nodes.
> Running with only 3 nodes isn't a great idea. Since a core purpose of Riak
> is to remain available in the face of outages, 3 will not support any
> outage. Less than 3 is lower than the default replication value (N=3). This
> is so important, in fact, that we recommend 5 solely to act as a buffer in
> the case where 1 of the 5 is down, the remaining 4 is dangerously close to
> the inflexible 3 node number. Even if you do not upgrade to 1.3, you really
> need to have at least 5 nodes.
> There are many benefits to upgrading to 1.3, but one of the most
> compelling from an operations point of view is active anti-entropy (AAE).
> Rather than waiting on read-repair to fix inconsistent values (which is
> passive), AAE routinely attempts to keep all node values in sync. This can
> be a godsend if a node goes down, since you don't need to fore read-repair
> when you bring the node back up by reading every key... you just let your
> cluster actively self-heal.
> Also on the 3 three nodes, the file size for the bitcask directory very
> quite a bit: 21GB, 14GB, and 20GB. Could the node with only 14GB missing
> something or it's expected to have such big difference?
> There are several reasons sizes could be different. Values are not
> yet/ever replicated (based on your N and W values). Files may have not been
> compacted. Some keys have been deleted but not yet reaped...
> Thanks,
> Tom
> --
> Tom Zeng
> Director of Engineering
> Intridea, Inc. |
> tom at
> (o) 888.968.4332 x519
> (c) 240-643-8728
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