Asynchronous AOF fsync is taking too long (disk is busy?). Writing the AOF buffer without waiting for fsync to complete, this may slow down Redis.

一、问题描述

Redis日志：

2110:M 24 Apr 02:01:02.058 * Asynchronous AOF fsync is taking too long (disk is busy?). Writing the AOF buffer without waiting for fsync to complete, this may slow down Redis.
2110:M 24 Apr 02:01:12.862 # Connection with slave client id #58526360 lost.
2110:M 24 Apr 02:01:12.863 # Connection with slave client id #58525913 lost.

sentinal日志：

788:X 24 Apr 02:01:07.970 # +sdown master mymaster 172.16.158.87 6379
1788:X 24 Apr 02:01:08.036 # +odown master mymaster 172.16.158.87 6379 #quorum 2/2
1788:X 24 Apr 02:01:08.037 # +new-epoch 79
1788:X 24 Apr 02:01:08.037 # +try-failover master mymaster 172.16.158.87 6379
1788:X 24 Apr 02:01:12.864 # +vote-for-leader fd5c6228b4f209cfc2c88265a0d47f39879027ab 79
1788:X 24 Apr 02:01:12.865 # +config-update-from sentinel 913c8b2f64f54caf46ff25ac6fa9bdcae86d9d02 172.16.158.85 26379 @ mymaster 172.16.158.87 6379
1788:X 24 Apr 02:01:12.865 # +switch-master mymaster 172.16.158.87 6379 172.16.158.85 6379
1788:X 24 Apr 02:01:12.865 * +slave slave 172.16.158.86:6379 172.16.158.86 6379 @ mymaster 172.16.158.85 6379
1788:X 24 Apr 02:01:12.865 * +slave slave 172.16.158.87:6379 172.16.158.87 6379 @ mymaster 172.16.158.85 6379
1788:X 24 Apr 02:01:12.867 # 913c8b2f64f54caf46ff25ac6fa9bdcae86d9d02 voted for 913c8b2f64f54caf46ff25ac6fa9bdcae86d9d02 79

监控截图

二、问题原因分析

参考：https://www.cnblogs.com/yangxiaoyi/p/7806406.html

参考：https://blog.csdn.net/ljl890705/article/details/51540427

三、解决操作(未验证)

1.修改sysctl vm.dirty_bytes内核参数

echo "vm.dirty_bytes=33554432" >> /etc/sysctl.conf　　
sysctl -p

2.修改Redis配置参数 repl-backlog-size

 repl-backlog-size=200mb