Making User-Managed Backups in S…

Making User-Managed Backups in SUSPEND Mode
This section contains the following topics:
■ About the Suspend/Resume Feature
■ Making Backups in a Suspended Database
About the Suspend/Resume Feature
Some third-party tools allow you to mirror a set of disks or logical devices, that is,
maintain an exact duplicate of the primary data in another location, and then<wbr> split the<br> mirror . Splitting the mirror involves separating the copies so that you can use them<br> independently.<br> With the SUSPEND/ RESUME<wbr> functionality, you can suspend I/O to the database, then<br> split the mirror and make a backup of the split mirror. By using this feature, which<br> complements the backup mode functionality, you can suspend database I/Os so that<br> no new I/O can be performed. You can then access the suspended database to make<br> backups without I/O interference.<br> You do not need to use SUSPEND/ RESUME<wbr> to make split mirror backups in most cases,<br> although it is necessary if your system requires the database cache to be free of dirty<br> buffers before a volume can be split. Some<wbr> RAID devices benefit from suspending<br> writes while the split operation is occurring; your RAID vendor can advise you on<br> whether your system would benefit from this feature.<br> The<wbr> ALTER<wbr> SYSTEM<wbr><wbr> SUSPEND statement suspends the database by halting I/Os to<br> datafile headers, datafiles, and control fi les. When the database is suspended, all<br> pre-existing I/O operations can complete; however, any new database I/O access<br> attempts are queued.<br> The<wbr> ALTER<wbr> SYSTEM<wbr><wbr> SUSPEND and ALTER SYSTEM<wbr><wbr> RESUME<wbr> statements operate on the<br> database and not just the instance. If the<wbr> ALTER SYSTEM<wbr> SUSPEND statement is entered<br> on one system in a RAC configuration, then the internal locking mechanisms<br> propagate the halt request across instances, thereby suspending I/O operations for all<br> active instances in a given cluster.<br> Making Backups in a Suspended Database<br> After a successful database suspension, you can back up the database to disk or break<br> the mirrors. Because suspending a database does not guarantee immediate termination<br> of I/O, Oracle recommends that you precede the<wbr> ALTER<wbr> SYSTEM<wbr><wbr> SUSPEND statement<br> with a BEGIN<wbr> BACKUP<wbr> statement so that the tablespaces are placed in backup mode.<br> You must use conventional user-managed ba ckup methods to back up split mirrors.<br> RMAN cannot make database backups or copies because these operations require<br> reading the datafile headers. After the database backup is finished or the mirrors are<br> re-silvered, then you can resume normal database operations using the<wbr> ALTER SYSTEM <wbr><br> RESUME<wbr> statement.<br> See Also: Oracle Database Reference for more information about the<br> data dictionary views<br> Making User-Managed Backups in SUSPEND Mode<br> 17-14 Backup and Recovery Advanced User’s Guide<br> Backing up a suspended database without splitting mirrors can cause an extended<br> database outage because the database is inaccessible during this time. If backups are<br> taken by splitting mirrors, however, then<wbr> the outage is nominal. The outage time<br> depends on the size of cache to flush, the number of datafiles, and the time required to<br> break the mirror.<br> Note the following restrictions for the<wbr> SUSPEND/RESUME feature:<br> ■ In a RAC configuration, you should not start a new instance while the original<br> nodes are suspended.<br> ■ No checkpoint is initiated by the ALTER SYSTEM<wbr><wbr> SUSPEND or<wbr> ALTER<wbr> SYSTEM <wbr><br> RESUME<wbr> statements.<br> ■ You cannot issue<wbr> SHUTDOWN<wbr> with<wbr> IMMEDIATE,<wbr> NORMAL , or<wbr> TRANSACTIONAL <wbr><br> options while the database is suspended.<br> ■ Issuing<wbr> SHUTDOWN<wbr><wbr> ABORT on a database that was already suspended reactivates<br> the database. This prevents media recovery or crash recovery from hanging.<br> To make a split mirror backup in SUSPEND mode:<br> 1. Place the database tablespaces in backup mode. For example, to place tablespace<br> users in backup mode enter:<br> ALTER TABLESPACE users BEGIN BACKUP;<br> If you are backing up all of the tablespaces for your database, you can instead use:<br> ALTER DATABASE BEGIN BACKUP;<br> 2. If your mirror system has problems with splitting a mirror while disk writes are<br> occurring, then suspend the database. For example, issue the following:<br> ALTER SYSTEM SUSPEND;<br> 3. Check to make sure that the database is suspended by querying V$INSTANCE. For<br> example:<br> SELECT DATABASE_STATUS FROM V$INSTANCE;<br> DATABASE_STATUS<br> -----------------<br> SUSPENDED<br> 4. Split the mirrors at the operating system or hardware level.<br> 5. End the database suspension. For example, issue the following statement:<br> ALTER SYSTEM RESUME;<br> 6. Check to make sure that the database is active by querying V$INSTANCE. For<br> example, enter:<br> SELECT DATABASE_STATUS FROM V$INSTANCE;<br> DATABASE_STATUS<br> -----------------<br> ACTIVE<br> 7. Take the specified tablespaces out of backup mode. For example, enter the<br> following to take tablespace<wbr> users out of backup mode:<br> ALTER TABLESPACE users END BACKUP<br> 8. Copy the control file and archive the online redo logs as usual for a backup.<br></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>