IBM®
Db2® server
suspended I/O support enables you to split mirrored copies of your primary database without taking
the database offline. You can use this to very quickly create a standby database to take over if the
primary database fails.
Disk mirroring is the process of writing data to two separate hard disks at the same time. One
copy of the data is called a mirror of the other. Splitting a mirror is the process of separating
the two copies.
You can use disk mirroring to maintain a secondary copy of your primary database. You can use
Db2 server
suspended I/O functionality to split the primary and secondary mirrored copies of the database
without taking the database offline. Once the primary and secondary databases copies are split, the
secondary database can take over operations if the primary database fails.
If you would rather not back up a large database using the
Db2 server backup
utility, you can make copies from a mirrored image by using suspended I/O and the split mirror
function. This approach also:
- Eliminates backup operation overhead from the production machine
- Represents a fast way to clone systems
- Represents a fast implementation of idle standby failover. There is no initial restore
operation, and if a rollforward operation proves to be too slow, or encounters errors,
reinitialization is very fast.
Important: It is required to suspend IO using the SET WRITE SUSPEND command, when taking
a split mirror copy of the database while the database is online. The use of a split mirror copy
without suspending IO (while the database is online) is not supported. Using such mirror copy can
result in data corruption, and such corruption can be very difficult to detect.
The
db2inidb command initializes the split mirror so that it can be used:
- As a clone database
- As a standby database
- As a backup image
This command can only be issued against a split mirror, and it must be run before the split
mirror can be used.
In a partitioned database environment, you do not have to suspend I/O writes on all database
partitions simultaneously. You can suspend a subset of one or more database partitions to create
split mirrors for performing offline backups. If the catalog partition is included in the subset, it
must be the last database partition to be suspended.
In a partitioned database environment, the
db2inidb command must be run on
every database partition before the split image from any of the database partitions can be used. The
tool can be run on all database partitions simultaneously using the
db2_all
command. If; however, you are using the
RELOCATE USING option, you cannot use the
db2_all command to run
db2inidb on all of the database
partitions simultaneously. A separate configuration file must be supplied for each database
partition, that includes the NODENUM value of the database partition being changed. For example, if
the name of a database is being changed, every database partition will be affected and the
db2relocatedb command must be run with a separate configuration file on each
database partition. If containers belonging to a single database partition are being moved, the
db2relocatedb command only needs to be run once on that database partition.
Note: Ensure that the split mirror contains all containers and directories which comprise the
database, including the volume directory. To gather this information, refer to the DBPATHS
administrative view, which shows all the files and directories of the database that need to be
split.