When using ZFS replication to provide a constant copy of your data, ensure that you can recover your tables, either manually or automatically, in the event of a failure of the original system.
In the event of a failure, follow this sequence:
Stop the script on the source, if it is still up and running.
Set the replica file system to be read/write:
#> zfs set readonly=off slavepool
Start up mysqld on the replica. If you are using
InnoDB, you get auto-recovery, if it is needed, to make sure the table data is correct, as shown here when I started up from our mid-INSERT snapshot:
InnoDB: The log sequence number in ibdata files does not match InnoDB: the log sequence number in the ib_logfiles! 081109 15:59:59 InnoDB: Database was not shut down normally! InnoDB: Starting crash recovery. InnoDB: Reading tablespace information from the .ibd files... InnoDB: Restoring possible half-written data pages from the doublewrite InnoDB: buffer... 081109 16:00:03 InnoDB: Started; log sequence number 0 1142807951 081109 16:00:03 [Note] /slavepool/mysql-5.0.67-solaris10-i386/bin/mysqld: ready for connections. Version: '5.0.67' socket: '/tmp/mysql.sock' port: 3306 MySQL Community Server (GPL)
InnoDB tables and a regular
synchronization schedule to reduce the risk for significant data
loss. On MyISAM tables, you might need to run
REPAIR TABLE, and you might even
have lost some information.