Question: How does the alter
system suspend database command work?
Answer:
The alter system suspend mode is used to stop all
I/O against your Oracle database, and the alter system
suspend is normally used when you want to take a backup
of Oracle with a cold backup with a mirrored database.
Because alter system suspend
does not guarantee immediate termination of I/O, Oracle
recommends that you precede the
alter system suspend
command with a begin backup command
so that the tablespaces are placed in backup mode before
suspending I/O..
select
database_status
from
v$instance;
database_status
-----------------
suspended
After you manually split the mirrors,
you can take the full backup and then re-synchronize the
mirrors. Following this operation, you can re-activate
the database with the alter system resume command.
The Oracle documentation issues the
following caveats on the alter system suspend
command:
"You do not need to use SUSPEND/RESUME to
make split mirror backups, unless your system requires the
database cache to be free of dirty buffers before a volume
can be split.
Some RAID devices benefit from
suspending writes while the split operation is occurring;
your RAID vendor can advise you on whether your system would
benefit from this feature. . . .
If the ALTER SYSTEM SUSPEND statement is
entered on one system in an Oracle RAC configuration, then
the internal locking mechanisms propagate the halt request
across instances, thereby suspending I/O operations for all
active instances in a given cluster."
