#不需要加--wsrep-new-cluster /usr/local/pxc_56/bin/mysqld_safe --defaults-file=/home/mysql/I6000/my6000.cnf --ledir=/usr/local/pxc_56/bin/ &
整个过程大约如下：
1.决断是否可以IST
2.不可以的话Requesting state transfer
3.Cleaning the existing datadir and innodb-data/log directories 会将之前实例的内容全部删除。#所以不能将my6000.cnf文件放在与datadir目录下，要不会被删除，并且在重新启动服务时出错
4.Waiting for SST streaming to complete
5.启动服务。
官方说明：
XtraBackup SST works in two stages:
• Stage I on joiner checks if it is SST or IST based on presence of xtrabackup_ist file.
• In Stage II it starts the data transfer, if it’s SST, it empties the data directory sans few files (galera.cache, sst_in_progress, grastate.dat) and then proceed with the SST or if it’s IST, proceeds as before.