Database Reference
In-Depth Information
Case Study
In this section we will simulate the failure of all voting disks in a RAC environment in order to
create a scenario for the removal of the RAC option. Did you know that an ORACLE instance,
which uses an
oracle
executable with RAC linked in, cannot be started irrespective of the value
of the
CLUSTER_DATABASE
parameter when cluster group services—a component of Oracle Clus-
terware—on the local node is not functional? This is true for ASM as well as RDBMS instances
(parameter
instance_type={ASM|RDBMS}
).
Simulating Voting Disk Failure
Voting disks are devices that Oracle Clusterware uses to ensure the integrity of the database in
case of an interconnect failure. Say you lose all the voting disks configured for use with Oracle
Clusterware. This causes Oracle Clusterware to abort. Following is a quick test that simulates
the failure of all voting disks. In this case, all voting disks means just one, since external
redundancy, that is, redundancy in the storage subsystem, is used instead of triple mirroring
by Oracle Clusterware. The test was performed on Red Hat Advanced Server 4.
Linux does not have proper raw devices. Instead the command
raw
must be used to bind
raw devices to block devices.
1
Failure of a voting disk may be simulated by binding the voting
disk device to an unused block device. On the test system,
/dev/md1
was such a device. It could
be opened without error, but 0 bytes were returned. The individual steps to simulate voting
disk failure are reproduced here:
1 # wc -c /dev/md1
2 0 /dev/md1
3 # crsctl query css votedisk # ask Clusterware for configured voting disks
4 0. 0 /opt/oracle/votedisk
5 located 1 votedisk(s).
6 # ls -l /opt/oracle/votedisk # character special device with major nr. 162
7 crw-r--r-- 1 oracle oinstall 162, 1 Jul 20 22:40 /opt/oracle/votedisk
8 # raw -q /opt/oracle/votedisk # which block device is it bound to?
9 /dev/raw/raw1: bound to major 8, minor 8
10 # ls -l /dev/sda8 # major device number 8 and minor 8 is sda8 (SCSI disk)
11 brw-rw---- 1 root disk 8, 8 Jul 24 03:15 /dev/sda8
12 # raw /opt/oracle/votedisk /dev/md1 # rebind to the wrong device
13 /dev/raw/raw1: bound to major 9, minor 1
14 # crsctl start crs
15 Attempting to start CRS stack
16 The CRS stack will be started shortly
17 # crsctl check crs
18 Failure 1 contacting CSS daemon
19 Cannot communicate with CRS
20 Cannot communicate with EVM
1.
ASM instances in Oracle10
g
Release 2 for Linux also support block devices, since the implementation
of raw devices is deprecated. Red Hat encourages software vendors to modify their applications to
open block devices with the
O_DIRECT
flag instead of requiring raw devices.
