Role of "innodb_fast_shutdown" (very useful for DBA) in case of MySQL Database Disaster

innodb_fast_shutdown - This is the Innodb shutdown mode and it is a Dynamic variable.

innodb_fast_shutdown=0; (slow shutdown)

If innodb_fast_shutdown is set to 0, the log files are purged when mysqld shuts down - larger files mean a longer shutdown time.

innodb_fast_shutdown=1 (default)
The default for innodb_fast_shutdown is 1, which means that the log files are not purged before a shutdown.

innodb_fast_shutdown=2 (Fast shutdown but may take longer startup)
A value is 2 simulates a crash, and at the next startup InnoDB will do a crash recovery.

This can be useful when testing to see approximately how long InnoDB takes to recover from a crash, to determine if the size of your log files is too large.