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From Laxmikant Upadhyay <laxmikant....@gmail.com>
Subject Re: Changing existing Cassandra cluster from single rack configuration to multi racks configuration
Date Tue, 12 Mar 2019 05:51:37 GMT
Hi Alex,

Regarding your below point the admin need to take care of temporary uneven
distribution of data util the entire process is done:

"If you can't, then I guess you can for each node (one at a time),
decommission it, wipe it clean and re-bootstrap it after setting the
appropriate rack."

I believe while doing so in the existing single rack cluster, the first new
node joined with different rack (rac2) will get 100% loaded in terms so
disk usage will be proportionally very high in comparison to other nodes in
rac1.
So until both racks have equal number of nodes and we run nodetool cleaup,
the data will not be equally distributed.


On Wed, Mar 6, 2019 at 5:50 PM Alexander Dejanovski <alex@thelastpickle.com>
wrote:

> Hi Manish,
>
> the best way, if you have the opportunity to easily add new
> hardware/instances, is to create a new DC with racks and switch traffic to
> the new DC when it's ready (then remove the old one). My co-worker Alain
> just wrote a very handy blog post on that technique :
> http://thelastpickle.com/blog/2019/02/26/data-center-switch.html
>
> If you can't, then I guess you can for each node (one at a time),
> decommission it, wipe it clean and re-bootstrap it after setting the
> appropriate rack.
> Also, take into account that your keyspaces must use the
> NetworkTopologyStrategy so that racks can be taken into account. Change the
> strategy prior to adding the new nodes if you're currently using
> SimpleStrategy.
>
> You cannot (and shouldn't) try to change the rack on an existing node (the
> GossipingPropertyFileSnitch won't allow it).
>
> Cheers,
>
> On Wed, Mar 6, 2019 at 12:15 PM manish khandelwal <
> manishkhandelwal03@gmail.com> wrote:
>
>> We have a 6 node Cassandra cluster in which all the nodes  are in same
>> rack in a dc. We want to take advantage of "multi rack" cluster (example:
>> parallel upgrade on all the nodes in same rack without downtime). I
>> would like to know what is the recommended process to change an existing
>> cluster with single racks configuration to multi rack configuration.
>>
>>
>> I want to introduce 3 racks with 2 nodes in each rack.
>>
>>
>> Regards
>> Manish
>>
>> --
> -----------------
> Alexander Dejanovski
> France
> @alexanderdeja
>
> Consultant
> Apache Cassandra Consulting
> http://www.thelastpickle.com
>


-- 

regards,
Laxmikant Upadhyay

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