Using Oracle Flex ASM with single instance database

Friday, July 25, 2014

Oracle Flex ASM was introduced in 12c version. This is one of the best features introduced with new version in my opinion.

I won’t speak in detail about Flex ASM because you can find more information in documentation. In this post I will concentrate on how Flex ASM handles crash of ASM instance.

For this test I’ve created 2 node cluster - 12c Grid Infrastructure with Flex ASM enabled.

$ asmcmd showclustermode
ASM cluster : Flex mode enabled

$ srvctl config asm ASM home: /u01/app/12.1.0/grid_1 Password file: +OCRVOTE/ASM/PASSWORD/pwdasm.256.853771307 ASM listener: LISTENER ASM instance count: ALL Cluster ASM listener: ASMNET1LSNR_ASM
$ srvctl status asm ASM is running on cluster1,cluster2


Install single instance database on one of the nodes.

$ ./dbca -silent \
> -createDatabase \
> -templateName General_Purpose.dbc \
> -gdbName singl12 \
> -sid singl12 \
> -sysPassword oracle \
> -SystemPassword oracle \
> -emConfiguration none \
> -recoveryAreaDestination FRA \
> -storageType ASM \
> -asmSysPassword oracle \
> -diskGroupName DATA \
> -characterSet AL32UTF8 \
> -nationalCharacterSet AL16UTF16 \
> -totalMemory 768 \

Copying database files 1% complete 3% complete 10% complete 17% complete 24% complete 31% complete 35% complete Creating and starting Oracle instance 37% complete 42% complete 47% complete 52% complete 53% complete 56% complete 58% complete Registering database with Oracle Restart 64% complete Completing Database Creation 68% complete 71% complete 75% complete 85% complete 96% complete 100% complete Look at the log file "/u01/app/orcl12/cfgtoollogs/dbca/singl12/singl12.log" for further details.


Single instance database is registered to the OCR.

$ srvctl config database -d singl12
Database unique name: singl12
Database name: singl12
Oracle home: /u01/app/orcl12/product/12.1.0/dbhome_1
Oracle user: orcl12
Spfile: +DATA/singl12/spfilesingl12.ora
Password file:
Domain:
Start options: open
Stop options: immediate
Database role: PRIMARY
Management policy: AUTOMATIC
Server pools: singl12
Database instance: singl12
Disk Groups: DATA
Mount point paths:
Services:
Type: SINGLE  <<<<<-------
Database is administrator managed

V$ASM_CLIENT shows that my database is managed by the Oracle ASM instance.

SQL> select instance_name, db_name, status
  2  from v$asm_client
  3  where db_name='singl12';

INSTANCE_NAME        DB_NAME  STATUS
-------------------- -------- ------------
singl12              singl12  CONNECTED


Check that ASM instances are running on both nodes.

$ ./crsctl status resource ora.asm
NAME=ora.asm
TYPE=ora.asm.type
TARGET=ONLINE            , ONLINE
STATE=ONLINE on cluster2, ONLINE on cluster1


My database is running on cluster1 node.

$ srvctl status database -d singl12
Instance singl12 is running on node cluster1

SQL> select instance_name, host_name from v$instance; INSTANCE_NAME HOST_NAME --------------- -------------------- singl12 cluster1.localdomain

Now I will simulate crash of ASM instance on cluster1 node where I have my database running.

# ps -ef|grep asm_pmon|grep -v grep
oracle    3072     1  0 10:12 ?        00:00:01 asm_pmon_+ASM1

# kill -9 3072

Without Flex ASM I would expect that crash of ASM instance would crash database instance also but with Flex ASM my database stays up and running.

Check alert log of database instance:
...
NOTE: ASMB registering with ASM instance as client 0x10005 (reg:2156157897)
NOTE: ASMB connected to ASM instance +ASM2 (Flex mode; client id 0x10005)
NOTE: ASMB rebuilding ASM server state
NOTE: ASMB rebuilt 1 (of 1) groups
NOTE: ASMB rebuilt 13 (of 13) allocated files
NOTE: fetching new locked extents from server
NOTE: 0 locks established; 0 pending writes sent to server
SUCCESS: ASMB reconnected & completed ASM server state

Check line - "NOTE: ASMB connected to ASM instance +ASM2 (Flex mode; client id 0x10005)"

As +ASM1 instance crashed ASMB connected to ASM instance +ASM2.


Check status:
# ./crsctl status resource ora.asm
NAME=ora.asm
TYPE=ora.asm.type
TARGET=ONLINE            , ONLINE
STATE=ONLINE on cluster2, INTERMEDIATE on cluster1


SQL> select instance_name, host_name from v$instance;

INSTANCE_NAME   HOST_NAME
--------------- --------------------
singl12         cluster1.localdomain

Oracle Clusterware restarted crashed ASM instance and both instances were up in a minute.

# ./crsctl status resource ora.asm
NAME=ora.asm
TYPE=ora.asm.type
TARGET=ONLINE            , ONLINE
STATE=ONLINE on cluster2, ONLINE on cluster1

Now to test crash ASM instance on second node.

SQL> select instance_name from v$instance;

INSTANCE_NAME
----------------
+ASM2

SQL> shutdown abort;
ASM instance shutdown

Excerpt from alertlog:

...
Fri Jul 25 12:44:33 2014
NOTE: ASMB registering with ASM instance as client 0x10005 (reg:4169355750)
NOTE: ASMB connected to ASM instance +ASM1 (Flex mode; client id 0x10005)
NOTE: ASMB rebuilding ASM server state
NOTE: ASMB rebuilt 1 (of 1) groups
NOTE: ASMB rebuilt 13 (of 13) allocated files
NOTE: fetching new locked extents from server
NOTE: 0 locks established; 0 pending writes sent to server
SUCCESS: ASMB reconnected & completed ASM server state


Again, user connected to database instance didn’t even noticed that something is happening with ASM.

Flex ASM enables for ASM instance to run on separate nodes than database servers. If ASM instance fails database will failover to another available ASM instance.

In case you are running <12c databases on your cluster you can still configure Flex ASM but you are required to configure local ASM instances on nodes. ASM instance failover won’t work for 10g or 11g databases.

Good reason to move towards 12c? ;-)




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2 comments:

  • As if the only issue with Rac instances crashing were crashing of ASM.

    This feature is hardly useful. Its another set of complicated code which means more bugs.
    RAC is becoming unnecessary almost in this virtualization era.

  • Marko Sutic

    You are running 12c RAC in production and you had problems with Flex ASM?

    Can you please show me some proof where RAC instance crashed due to bug/problem with Flex ASM?

    I'm not running 12c RAC with Flex ASM in production and I would be glad to learn more about possible problems.

    Please, share with me blog post, forum topic...

    Regards,
    Marko

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