Help with handling Riak disk failure

Leo scicomplete at gmail.com
Tue Sep 19 13:53:30 EDT 2017


Dear Bryan,

Thank you very much for your answers. They are very helpful to me.
I will use more nodes (>=5) in future.

>From your experience with using Riak, what would your guess be for the
time taken to finish all the AAE transfers and be done with the
recovery for about 1 TB worth of data (assuming my cluster is
otherwise completely idle without any user accessing the cluster
during this process and that  I am continuously watching the transfers
and re-enabling disabled AAE trees gradually )?  I am just asking for
rough estimate from your past experience ( please quote from your
experience with a difference sized cluster / data size too ). My guess
is that it will take approx. 2 days or more. Do you concur?

Thanks,
Leo


On Tue, Sep 19, 2017 at 12:41 PM, Bryan Hunt
<bryan.hunt at erlang-solutions.com> wrote:
> (0) Three nodes are insufficient, you should have 5 nodes
> (1) You could iterate and read every object in the cluster - this would also
> trigger read repair for every object
> (2) - copied from Engel Sanchez response to a similar question  April 10th
> 2014 )
>
> * If AAE is disabled, you don't have to stop the node to delete the data in
> the anti_entropy directories
> * If AAE is enabled, deleting the AAE data in a rolling manner may trigger
> an avalanche of read repairs between nodes with the bad trees and nodes
> with good trees as the data seems to diverge.
>
> If your nodes are already up, with AAE enabled and with old incorrect trees
> in the mix, there is a better way.  You can dynamically disable AAE with
> some console commands. At that point, without stopping the nodes, you can
> delete all AAE data across the cluster.  At a convenient time, re-enable
> AAE.  I say convenient because all trees will start to rebuild, and that
> can be problematic in an overloaded cluster.  Doing this over the weekend
> might be a good idea unless your cluster can take the extra load.
>
> To dynamically disable AAE from the Riak console, you can run this command:
>
>> riak_core_util:rpc_every_member_ann(riak_kv_entropy_manager, disable, [],
> 60000).
>
> and enable with the similar:
>
>> riak_core_util:rpc_every_member_ann(riak_kv_entropy_manager, enable, [],
> 60000).
>
> That last number is just a timeout for the RPC operation.  I hope this
> saves you some extra load on your clusters.
>
> (3) That’s going to be :
> (3a) List all keys using the client of your choice
> (3b) Fetch each object
>
> https://www.tiot.jp/riak-docs/riak/kv/2.2.3/developing/usage/reading-objects/
>
> https://www.tiot.jp/riak-docs/riak/kv/2.2.3/developing/usage/secondary-indexes/
>
>
>
>
>
>
>
> On 19 Sep 2017, at 18:31, Leo <scicomplete at gmail.com> wrote:
>
> Dear Riak users and experts,
>
> I really appreciate any help with my questions below.
>
> I have a 3 node Riak cluster with each having approx. 1 TB disk usage.
> All of a sudden, one node's hard disk failed unrecoverably. So, I
> added a new node using the following steps:
>
> 1) riak-admin cluster join 2) down the failed node 3) riak-admin
> force-replace failed-node new-node 4) riak-admin cluster plan 5)
> riak-admin cluster commit.
>
> This almost fixed the problem except that after lots of data transfers
> and handoffs, now not all three nodes have 1 TB disk usage. Only two
> of them have 1 TB disk usage. The other one is almost empty (few 10s
> of GBs). This means there are no longer 3 copies on disk anymore. My
> data is completely random (no two keys have same data associated with
> them. So, compression of data cannot be the reason for less data on
> disk),
>
> I also tried using the "riak-admin cluster replace failednode newnode"
> command so that the leaving node handsoff data to the joining node.
> This however is not helpful if the leaving node has a failed hard
> disk. I want the remaining live vnodes to help the new node recreate
> the lost data using their replica copies.
>
> I have three questions:
>
> 1) What commands should I run to forcefully make sure there are three
> replicas on disk overall without waiting for read-repair or
> anti-entropy to make three copies ? Bandwidth usage or CPU usage is
> not a huge concern for me.
>
> 2) Also, I will be very grateful if someone lists the commands that I
> can run using "riak attach" so that I can clear the AAE trees and
> forcefully make sure all data has 3 copies.
>
> 3) I will be very thankful if someone helps me with the commands that
> I should run to ensure that all data has 3 replicas on disk after the
> disk failure (instead of just looking at the disk space usage in all
> the nodes as hints)?
>
> Thanks,
> Leo
>
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