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From Joshua Galbraith <>
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:

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 <>

> 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
> 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 <>
> 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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