Hello, It is very hard to estimate the time to encrypt all that data. That is the reason we don't use any table or reference for the time that will take. On the other hand, you should always perform an operation like that, on a low period for your cluster usage to reduce impact - https://docs.aws.amazon.com/redshift/latest/mgmt/changing-cluster-encryption.html On performance, per my experience there is not a significant impact but the best option is for you to turn encryption on, test and if it doesn't fit your needs, to turn it off.
please, also keep in mind to use datashare you have to be running on RA3 node types to support this operation.
Hope it helps!
It is hard to estimate the exact time but The faster Classic resize feature enables an unencrypted cluster to encrypt it much more quickly.
As of today, the Faster Classic Resize option to restore an unencrypted snapshot into an encrypted cluster or to change the encryption key is available only through the AWS CLI. When triggered, the restored cluster operates in read/write mode immediately. The encryption state change for restored blocks that are unencrypted operates in the background, and newly ingested blocks continue to be encrypted. Please refer to the following blog. https://aws.amazon.com/blogs/big-data/accelerate-resize-and-encryption-of-amazon-redshift-clusters-with-faster-classic-resize/
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