Two slaves using the same server-id
The server ID is used for replication to enable master and slave servers to identify themselves, uniquely. While replication may work if two slaves have the same server ID, it could affect performance. Also, having them all unique can provide help in managing and monitoring the MySQL servers participating in the replication. Currently, a MySQL master server allows slaves with the same server-ID. This is a known problem, and could cause slaves to make several smaller relay logs files. Closing and opening files as a result will consequently slow down the replication process.