Help with handling Riak disk failure

Bryan Hunt bryan.hunt at erlang-solutions.com
Tue Sep 19 15:23:10 EDT 2017


Sorry Leo, 

That’s completely impossible to guess :-D 

Factors include - I/O, Network cards, network switch, selinux, block size, CPU, size of objects, number of objects, CRDT, Riak version, etc… 

Best, 

Bryan 

> On 19 Sep 2017, at 18:53, Leo <scicomplete at gmail.com> wrote:
> 
> 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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>> riak-users at lists.basho.com
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>> 
>> 





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