Restarting a DS is a safe procedure. It will not affect ingest, there will be no loss of data.
You should however note that:
If you are publishing a new application (which will be distributed to DS clients) which has the restart splunk flag set, this will cause the client forwarders to restart the Splunk process.
Generally speaking, this is not too much of a concern, however if you have forwarders (affected by the new app you are distributing) which process stateless data (such as TCP/UDP inputs) or run scripted inputs, you should be aware that there will be a disruption to these mechanisms for the few minutes it takes to restart Splunk.
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