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From Joshua Galbraith <jgalbra...@newrelic.com.INVALID>
Subject Re: Switching Snitch
Date Sun, 26 Aug 2018 18:34:59 GMT
Pradeep, it sounds like what you're proposing counts as a topology change
because you are changing the datacenter name and rack name.

Please refer to the documentation here about what to do in that situation:
https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsSwitchSnitch.html

In particular:

Simply altering the snitch and replication to move some nodes to a new
> datacenter will result in data being replicated incorrectly.


Topology changes may occur when the replicas are placed in different places
> by the new snitch. Specifically, the replication strategy places the
> replicas based on the information provided by the new snitch.


If the topology of the network has changed, but no datacenters are added:
> a. Shut down all the nodes, then restart them.
> b. Run a sequential repair and nodetool cleanup on each node.


On Sun, Aug 26, 2018 at 11:14 AM, Pradeep Chhetri <pradeep@stashaway.com>
wrote:

> Hello everyone,
>
> Since i didn't hear from anyone, just want to describe my question again:
>
> Am i correct in understanding that i need to do following steps to migrate
> data from SimpleSnitch to GPFS changing datacenter name and rack name to
> AWS region and Availability zone respectively
>
> 1) Update the rack and datacenter fields in cassandra-rackdc.properties
> file and rolling restart cassandra with this flag
> "-Dcassandra.ignore_dc=true -Dcassandra.ignore_rack=true"
>
> 2) Run nodetool repair --sequential and nodetool cleanup.
>
> 3) Rolling restart cassandra removing the flag  "-Dcassandra.ignore_dc=true
> -Dcassandra.ignore_rack=true"
>
> Regards,
> Pradeep
>
> On Thu, Aug 23, 2018 at 10:53 PM, Pradeep Chhetri <pradeep@stashaway.com>
> wrote:
>
>> Hello,
>>
>> I am currently running a 3.11.2 cluster in SimpleSnitch hence the
>> datacenter is datacenter1 and rack is rack1 for all nodes on AWS. I want to
>> switch to GPFS by changing the rack name to the availability-zone name and
>> datacenter name to region name.
>>
>> When I try to restart individual nodes by changing those values, it
>> failed to start throwing the error about dc and rack name mismatch but
>> gives me an option to set ignore_dc and ignore_rack to true to bypass it.
>>
>> I am not sure if it is safe to set those two flags to true and if there
>> is any drawback now or in future when i add a new datacenter to the
>> cluster. I went through the documentation on Switching Snitches but didn't
>> get much explanation.
>>
>> Regards,
>> Pradeep
>>
>>
>>
>>
>>
>>
>>
>>
>


-- 
*Joshua Galbraith *| Lead Software Engineer | New Relic

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