It was actually funny. So thought about posting it that sometimes how we can miss the absolute basics. This customer is using a virtualized Exadata with multiple VMs. One VM hosts the database meant to be used for dbfs and another VM connects to this DB over IB to mount dbfs file system using dbfs_client. One day VMs were rebooted and due to some reason the dbfs filesystem didn’t mount on startup. It went on for few days and they couldn’t mount it. One day I got a chance to look at it and the error they were facing was:
File system already present at specified mount point /dbfs_direct
If you are familiar with Unix, this clearly indicates some problem with the directory where it is trying to mount the file system. I checked that and there were some files in /dbfs_direct. I moved those files and it was able to mount. Issue resolved.
Then after closing the session, I was thinking that what could have happened as this dbfs mount point has been in use for long. Then it struck me. It was being used to take some RMAN backups and the path was hard coded in the scripts. When it didn’t mount after the reboot (i don’t know why), someone ran that script and whatever directories it didn’t find, it probably created that complete directory structure and tried to write to a log file. Once /dbfs_direct had those files, it anyway was not going to mount.
Earlier versions of OEDA didn’t allow you to have mixed cells in the configuration i.e. High Capacity (HC) and Extreme Flash (EF). The way to deal with that configuration was that deploy the system with either HC or EF cells and then manually configure the remaining cells.
I am not sure when did it change but the newer versions allow you have mixed type of cells in a single OEDA configuration. Once you select the hardware, there is an additional option called Enable Additional Storage, where you can select the other type of cells. The minimum number of cells has to be three to use this option. Also the cells that are at the bottom of the rack physically should be selected as main storage and the other cells should be added as additional storage as that is how OEDA builds the configuration files.
Once this is selected, on the Diskgroups screen, select Diskgroup layout as custom and you can create multiple diskgroups and select cells for each diskgroup (as EF & HC cells can’t be part of the same diskgroup).
Once the configuration is generated, it can be deployed with OneCommand without any manual intervention. A small feature but makes life easier by getting rid of all the manual steps.
A quick note about an error I faced while running root.sh on an Exadata machine. The configuration tools failed with the following error:
Error is PRVF-4657 : Name resolution setup check for "db-scan" (IP address: x.x.x.101) failed
I did nslookup on the scan name and it all seemed good. So why the error ? After spending another 5 minutes, I looked at /etc/hosts and there was it. Someone had populated /etc/hosts of DB nodes with all the hostnames entries including the scan name. Something like:
As /etc/hosts can return only one IP against a hostname whereas for scan, DNS is supposed to return 3 IPs, hence the problem. The solution is to comment out the scan name entries in /etc/hosts on all the db nodes and let the system do the name resolution via the DNS.
Exadata storage software version 20.1 introduces a new feature called “Secure Fabric” for KVM based multi cluster deployments (Exadata X8M). It enables network isolation between multiple tenants (i.e. KVM VMs based RAC clusters). This feature aligns with Infiniband Partitioning on OVM based systems. There are customers who in such scenarios want that VMs of one RAC shouldn’t be able to see traffic of the other RAC VMs. This feature achieves that. Similar to Pkeys in IB switches, here it uses a double VLAN tagging system where the first tag identiefies the network partition and the second tag is used to denote membership level of the VM. Exadata documention has more details.
The minimum Exadata software version needed to enable this feature is 20.1. This release comes with RoCE switches firmware version 7.0(3)I7(8).
Starting Jun 2020, OEDA supports this configuraion and this feature can be enabled in OEDA itself. To enable it in OEDA, under Cluster Networks click on the Advanced button and you will see the Enable Secure Fabric option.
Once this option is enabled, you will see VLANs enabled for the private network. While doing the deployment, OneCommand will take care of the configuration needed.
As per documentation, at present there is no way to enable it on existing systems except doing a re-deployment.
There are two common scenarios when we may need this:
An existing DB node has crashed and is unrecoverable (due to some failure and non-availability of any backups. Though some of the things may need to be done even if the backups were available).
We have an existing Exadata rack that is virtualized. Now there is a new DB node and the existing clusters need to be extended to include the VMs on this new node.
I recently faced the first scenario where a virtualized DB node crashed and wasn’t recoverable. A bare metal DB node restore is a relatively simple procedure where we just have to reimage the node, create the needed directories, users etc and add it to the RAC cluster. In case of virtualization, the creation of VMs is an additional step that needs to be done. That makes it slightly more complex.
So the scenario is that we have an Exadata quarter rack where DB node1 has issues and needs to be reimaged and reconfigured. There are multiple VMs (so RAC clusters) created. As one of the DB node has gone down, each RAC cluster is running with one less instance. This failed node will need to be cleaned up from the RAC configuration before adding it back. Here are the steps that we need to follow to restore it back:
Reimage the node using an ISO and make it ready for creation of User Domains (aka VMs)
Create the required VMs
Create the required users, setup ssh with other nodes
Clear the failed node configuration from existing RAC clusters
Add the newly created VMs back to the respective RAC clusters
Now let’s discuss these steps in detail.
Reimage : The simplest way to reimage an Exadata node is to connect the ISO (We can download the ISO for the version we need from MOS note 888828.1) using ILOM, set the next boot device to CD-ROM, reboot/reset the node and let it boot from CD-ROM. Most of the installation part is automated and doesn’t ask any questions. Once it is done installing, ipconf starts in interactive mode and asks for all the information like Name servers, NTP servers, IP addresses and hostnames for various network interfaces etc. Once done, it will boot into the Linux partition. Since we need to virtualize the node, we need to switch it to OVS by running a script called /opt/oracle.SupportTools/switch_to_ovm.sh. It will reboot the node to OVS partition. Next step is to run reclaim /opt/opt/oracle.SupportTools/reclaim.sh -free -reclaim to reclaim the space used for bare metal partition. At this moment we are done with the reimaging part. To use ILOM in a browser and be able to access the console, we need a Java enabled Windows/Linux system. And if there is a firewall between that system and the server, this link lists the ports that need to be allowed in the firewall.
VMs creation : Next step is the creation of VMs. We will use OneCommand to achieve this. In this case, we had the original XML file used for deployment. Now we need to edit that configuration and remove the existing node’s details from it. We can import the XML into OEDA, make the required changes and save the configuration files. This needs to be done carefully as a simple mistake like a duplicate IP may cause issues with the ASM/DBs running on the other node. Once this is done, we can download the OneCommand patch (MOS note 888828.1) and run the create VMs step of OneCommand. As we have only one node in the XML file, so it is not going to touch the existing configuration.
Create users : Now we need to create the users on the newly created VMs. OneCommand’s create users step can be used here. It will create users on all the VMs. There are some things that we need to do manually here. First thing is to remove binaries from Grid & DB home. As we are going to use addnode.sh to add new nodes to existing RAC clusters, so binaries are going to be copied from an existing node. Then we need to change ownership of Grid & DB home directory tree to oracle:oinstall. Also for each VM, we need to setup passwordless ssh with the respective other VM (& vice versa) that is going to be part of the cluster.
Clear failed node config : Next we need to clear the failed node’s configuration from each of the RAC clusters. That is pretty much the standard stuff we do in RAC.
Add the new nodes : This again is just the standard addnode stuff we do in RAC.
I have used the terms VM and Node interchangeably here but the context should make it clear if I am referring to the physical node or a VM. There is another method to do this using OEDACLI and it is documented in Exadata documentation. That automates a lot of these things. Check this link for the details.