I am trying to find the best practices of running 'nodetool repair' as part of migrating large OnPrem Cassandra clusters to cloud, and decommissioning the old cluster.
The blog http://www.redshots.com/moving-cassandra-clusters-without-downtime---part-2/ suggests running full repair on each node of the new DC, but the Datastax documentation https://docs.datastax.com/en/dse/6.8/dse-admin/datastax_enterprise/operations/opsDecomissionDC.html doesn't say if we need to run on the old or new DC or to run on all nodes or a single node. I know, there are possibly multiple ways of running it, hence was looking for some guidance on how to best run nodetool repair as part of the decommission datacenter step.
My questions are -
1. Considering the fact that nodetool repair can be quite resource intensive, is there an alternate way to ensure data consistency, after we stop new writes to the old DC?
2. If running nodetool repair is the best option available to confirm all the data has migrated correctly from the original DC
a. Should we run it in the old DC or new DC?
b. Is it better to run one node at a time or running full repair?
I am looking for a safe way to run it with minimal impact to Production workload and application. Thanks for any guidance you can provide!