In a Serial 3-Server Replication Scenario (A>B>C), can server B preserve binlogs that server A has purged? This is in the service of a live migration, where server A has heavy performance and space demands, so I would like to keep down the amount of disk-space used by logs - let's say expire_logs_days = 10.

If I set server B, which is a slave of server A, to expire_logs_days = 30, will it then work to use a 20 day old snapshot (of B, for argument's sake) to make a new slave of B, called C, that will be able to catch up, or does the fact that server A has binlogs purged on the 10th day somehow break that scheme?

I am using row-based GTID replication on Percona 5.6, b.t.w.
No problem.


A (as a Master) writes to its binlog
That stuff is copied (usually immediately) to the "relay-log" on B (as a Slave).
That stuff is written to B's binlog
That stuff is copied to the relay log on C.


If the network from A to B goes down for more than 10 days, you will lose data.  For B to C, you have 30 days to repair the network, even though some stuff may no longer be in A's set of binlogs.

Another thing to note:  I think the purging of old binlogs does not occur until the current binlog exceeds its limit.  If that limit is large (in comparison to the activity), it could take days to roll over.  You might want to shrink the limit to get better granularity.  (And it is OK if A and B have different limits.)