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Sunday, November 28, 2010

My first 11gR2 RAC on VirtualBox - Learned Lessons

Oracle 11gR2 comes with many RAC goodies and, of course, I want to see them in action. But, the first step is to actually have a 11gR2 available. So, I decided to install one on my poor Dell PowerEdge 1850 server. As it turned out, even the installation process is changed with the introduction of the SCAN, GNS, server pools etc. However it makes this task more challenging, doesn't it?

Because this RAC was not intended to be used for any productive purposes my first choice was for a virtualized environment. I tried Oracle VM in the first place and I was quite disappointed about the results:

1. my virtual machines were reboting unexpectedly, even they were idle. I didn't managed to find the cause of this.

2. during heavy loads on my virtual machines I was constantly getting:

INFO: task kjournal:337 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_sec" disables this message.

I guess Oracle already fixed that but I don't have any ULN subscriptions, so no updates.

My next option was VirtualBox which is a nice choice and it is also provided by Oracle. VirtualBox supports now shared disks which makes it a very appealing solution for RAC testing. In addition, there's also a well written guide about how to install a RAC on VirtualBox here.

To summarize, below are the main lessons I learned out of this RAC installation process:

1. High CPU load for my virtual hosts: after I created the hosts which were supposed to act as RAC nodes, I noticed that the CPUs on the host server was on 100% even the guests were idle. My host server has 8G RAM and 2 physical CPU on 3.4GHz, so this high CPU consumption didn't feel right at all. The solution was to boot my virtual hosts with the divider=10 option. Even with this tweak the whole installation process was slow, so be prepared to wait...

2. pay attention to the groups membership for the oracle/grid users: I made a stupid mistake and I forgot to add the oracle user to asmdba group. The prerequisites checks didn't complained and I successfully installed the Grid Infrastructure and the Oracle database software. However, when I reached the database installation phase using dbca I noticed that no asm diskgroups were available even they were accessible on my "grid" user. So, in order to save precious time for debugging such tricky issues double check these groups membership requirements.

3. the time synchronization issue: because I wanted to use new stuff for my RAC I decided to get rid of the ntpd synchronization and to use the Oracle CTSSD implementation. However, be careful here. Oracle is peaky when it comes to detecting if other synchronization software is installed. Even your ntpd daemon is stopped you also have to remove/rename the /etc/ntpd.conf file. Otherwise, the time synchronization check will fail. And another thing: if you configure your NIC interfaces via DHCP you may end up having this /etc/ntpd.conf after every node reboot. In order to prevent this you may use static address initialization or you may add PEERNTPD=no to your ifcfg-ethX scripts.

4. GNS preparations: this GNS (Grid Naming Service) component is new in 11gR2 and is not a very tasty concept for those DBAs (like me) who do not have a lot of knowledge in network administration field. So, if you are going to use GNS, be sure you have an experienced system administrator around, to provide you support for configuring it. However, you still need to know what to ask him to do. Basically, you have to agree on a new DNS zone. If your company domain is you may choose for your RAC Then, you need to ask him to delegate the requests form * to an unallocated IP address from the same IP class as your future RAC public interface. This IP is the VIP for your GNS and it will be available only when your RAC installation is successfully finished. Then, your system administrator will ask you under which name to "glue" the new zone. He actually want to know under which DNS name to register this GNS vip address. The glue is really a well-known concept in the DNS terminology. As far as I noticed Oracle uses <cluster_name>-gns-vip.<gns_zone>. So, for our hypothetical example, assuming the rac name is "muci", the gns glue would be:

5. ORA-15081: I think this has to do with the membership mistake. DBCA was reporting ORA-15081, complaining that it cannot create stuff into ASM diskgroups. The metalink note 1084186.1 provides the solution.

Okey, that would be all. Happy (but slow) RAC on VirtualBox.


zielinski.bartosz said...

Hi Aleksanru

Do you have a problem with node eviction without any reason ?


Alexandru Tica said...

Hi Bartosz,

Just under OracleVM I noticed that, from time to time, one node was shouted down without any apparent reason.

Surachart said...

Good Post.
I installed 11gR2 RAC on Virtualbox and It OK... for test.
But CPU load.... maybe I should tune something :)