title: Does adding a redis slave issue a blocking call to the master?
body: <p>It is unclear to me from the <a href="http://redis.io/topics/replication" rel="nofollow">documentation on replication</a> whether the <a href="http://redis.io/commands/sync" rel="nofollow">SYNC command</a> is blocking.</p>
  
  <p>It seems like it shouldn't be (after all, spinning up a new slave would stop the <em>master</em> from serving requests), but I'd like confirmation of that.</p>
  
  <p>For context, I'm looking at adding a slave to a master hosting about 8GB of data with no disk sync*.</p>
  
  <p><sub>*Historically, data loss has not been a concern.  We're changing that, so replication and persistence are being "back ported" to a degree.</sub></p>