Expert Oracle Exadata - Parent Directory

CHAPTER 9 RECOVERING EXADATAWait EventsThere are two Exadata-specific wait events that are triggered by database backup and recoveryoperations on the Exadata platform; cell smart incremental backup, and cell smart restore frombackup. These wait events are covered in more detail in Chapter 10.cell smart incremental backup: This wait event occurs when Exadata offloadsincremental backup processing to the storage cells. The P1 column of theV$SESSION_WAIT view contains the cell hash number. This hash value can beused to compare the relative backup performance of each storage cell anddetermine if there is a performance problem on any of the cells.cell smart restore from backup: This wait event occurs during restoreoperations when Exadata offloads the task of initializing a file to the storagecells. The P1 column of V$SESSION_WAIT contains the cell hash number. Thishash value can be used to compare the relative restore performance of eachstorage cell and determine if there is a performance problem on any of the cells.Recovering ExadataA better title for this section might be, “When Things Go Wrong.” After all, that’s usually about the timewe realize how little practical experience we have recovering our systems. As corporate Americacontinues to squeeze every drop of productive time out of our work week, DBAs and SystemAdministrators spend most if not all of their waking hours (and sometimes sleeping hours) just “keepingthe wheels on.” So actually practicing system recovery is more often than not treated like the proverbial“red-headed step child”—seldom thought about, and rarely attended to. And even if we find ourselves inthe enviable position of having the time to practice system recovery, it’s rare to have the spareequipment to practice on. So kudos to you if you are reading this and nothing is actually broken. In thissection we’ll be discussing Exadata system recovery using the backup methods we covered in the“Backing Up Exadata” section of this chapter.Restoring the Database ServerBacking up and restoring the database servers can be done using third-party backup software orhomegrown scripts using familiar commands like tar and zip. Recently Oracle began configuring theExadata database servers with the Linux Logical Volume Manager (LVM), which provides snapshots forcreating point-in-time, tar-based backup sets. The procedure for recovering Exadata database servers isa very structured process that is specific to Exadata. In this section we’ll be stepping through thisprocedure presuming the backup was taken using the backup procedure discussed earlier in thischapter. So, if you haven’t read through that section of this chapter, you might want to take a look at itbefore continuing.Recovery Using LVM Snapshot-Based Backup ImagesRestoring the database server using the LVM snapshot backup procedure we discussed earlier in thischapter is a fairly straightforward process. The backup image we will use in this procedure,enkdb01_system_backup.tar.bz2, is the one we created earlier in this chapter and includes the /, /boot,and /u01 file systems. The first thing you need to do is stage the backup image on an NFS file system thatcan be mounted by the failed database server. The server is then booted from a special diagnostics ISO296