dbi Blog

The question to migrate or not to the Cloud comes more and more often now. There are some added values to go to the Cloud as analytics capabilities, scalability and flexibility, cost saving, no dedicated hardware and its related maintenance, no maintenance for patch, no worry to have about HA, DR or Data Protection. We can easily understand this. But on the other side, we can also wonder what will be the performance, what about my sensitive data, how to monitor the costs, the lock-in risk (am I married for ever or how high is the egress cost) and of course what will be the downtime of the migration. For this last point, the Oracle ZDM tool is going to help us. For some time now I have been wondering what is the easiest way and best way for customer to migrate to OCI, before hearing about Oracle Zero Downtime Migration. I wanted to have a closer look at it and test it. I would like, through this blog, to share some information I could gather about ZDM.

Oracle Cloud solutions

First of all, let’s have a quick and closer look to the Oracle Cloud Solutions available to manage my oracle databases. We are having the OCI with databases running on VM (Virtual Machine) or BM (Bare Metal) and autonomous databases. And we are having 3 offers based on Exadata : Exadata On-Premises, Exadat Cloud at Customer (ExaCC) and Exadata Cloud Service (ExaCS).

Exadata Machine on On-Premises:

This solution will fulfil my need for sensitive data with higher performance and availability requirements.
The exadata are installed in customer Data Center. The data are locally stored behind customer firewall.
The customer will manage every component including the HW.
There is no Cloud Services available.
This solution is based on purchased-based Model.
For Exadata X9M we are having 2 models. The X9M-2 with 2 sockets and the X9M-8 with 8 sockets. For example, for a X9M-8 Half Rack, I will have 2 DB servers giving a total of 384 cores, 3 storage server with a total of 98 cores, 648 TB of disk storage, 77 TB of flash storage and 4.5 TB of persistent memory. The Oracle datasheet for Exadata can be found here:
https://www.oracle.com/a/ocom/docs/engineered-systems/exadata/exadata-x9m-2-ds.pdf
https://www.oracle.com/a/ocom/docs/engineered-systems/exadata/exadata-x9m-8-ds.pdf

Exadata Cloud at Customer (ExaCC):

In this solution the Exadata will still be stored in the customer Data Center. So the data are still located on customer side behind the firewall.
But the customer will be only responsible to manage the Exadata VMs (DomU) and the Databases when Oracle will on its side manage the Exadata HW, firmware and hypervisor.
In case for Automomous Database Service subscription, Oracle will manage the full stack, that’s to say including the VMs and the DB. Customer will in that case only be responsible of his data.
Customer can benefit of Cloud Services.
Database are provisioned through the Oracle Cloud.
All data is encrypted and not visible to Oracle
The cost is based on hourly OCPU consumption and shape sizing.
This solution is based on subscription-based model

Exadata Cloud Service (ExaCS):

In this solution, the Exadata and customer’s data are stored on the Oracle’s Public Cloud.
The customer will in this case also be responsible to manage the Exadata VMs (DomU) and the Databases when Oracle will on its side manage the Exadata HW, firmware and hypervisor.
In case for Automomous Database Service subscription, Oracle will manage the full stack, that’s to say including the VMs and the DB. Customer will in that case only be responsible of his data.
Customer can benefit of Cloud Services.
The cost is based on pay-per-use model.
This solution is based on subscription-based model.

How can I migrate my databases to OCI?

There is several factors to take into account:

Database version
OS system and version
Character set
Among of database and indexes
Data Types in the on-premises database
Storage
Network bandwidth
Downtime length
Architecture CDB or Non-CDB
Endian format that can be found with the V$TRANSPORTABLE_PLATFORM view. OCI Database uses Linux platform (little endian)

There are then several migration methods available and that we can use:

DataPump (Export/Import, Tranportable, …)
Remote Cloning PDB or Non-CDB
RMAN Cross-Platform Transportable PDB, tablespace
RMAN Duplicate from Active Database
RMAN Convert Transportable Tablespace
SQL Developer
Plug/Unplug PDB or Non-CDB

And of course ZDM (Zero Downtime Migration) Oracle tool!

What is Oracle ZDM?

ZDM is Oracle’s premier solution for simplified and automated Oracle databases migration. It provides zero to negligible downtime for production system. That’s to say minimal to no production database impact during the migration. This tool will reduce the human errors.

The current version is Oracle ZDM 21.4.

Where can I migrate to with ZDM?

Oracle Exadata On-Premises
Oracle Exadata Cloud at Customer (ExaCC)
Oracle Exadata Cloud Service (ExaCS)
Oracle Database Cloud Infrastructure (BM and VM)
Oracle Cloud Autonomous Database (OTP and ADW)

Where can I migrate from?

On-Premises
Oracle Databases on AWS RDS (Relational Database Service)
Oracle Public Cloud Gen 1
Oracle Cloud Infrastructure (OCI)
Databases can be hosted on Linux, AIX and Solaris OS
Databases can be SI, RAC one Node or RAC Databases
Oracle Database Enterprise and Standard Edition
Non-CDB or CDB with one or more PDB

Source database version can be : 11.2.0.4, 12.1.0.2, 12.2.0.1, 18c, 19c, 21c.

ZDM will have following benefits:

Simple and Efficient with Oracle ZDM automated workflow
Highly Available
Flexible
Validation
Cost-Effective

Finally ZDM follows Oracle MAA (Maximum Availability Architecture) best practices with Golden Gate and Data Guard solutions. Online migration workflow will be using Recovery Manager, Data Pump and DB links.

Oracle ZDM Migration workflows

There is 7 Migration workflows we can use with ZDM. Some of those workflows are using backups.

In case backups are used, the initial backup of the source will use RMAN compression. What is nice with ZDM is that, while the migration is performed with ZDM and only in the purpose of the migration operation, Oracle Advanced Compression and Oracle Advanced Security licenses are granted and can be used for free. The advantage is that it will reduce the size of the backup, that is to say the amount of database being transported to the cloud. RMAN backups can be customized. In case we are migrating to on-prem, that’s to say, migrating to Exadata Machine or ExaCC, you can use existing backups, and none needs to be taken through ZDM. Also if using Zero Data Loss Recovery Appliance (ZDLRA), restore can be done directly from it without taking backups. For any other target platform (OCI, ExaCS, or Autonomous Database), ZDM will have to take backups itself as part of the workflow.

1- Physical Offline Migration

This workflow will support SE2 and EE database migration. It will use backup and restore through RMAN with a backup location that can be either an object storage, or a NFS file system or a ZDLRA (Oracle Zero Data Loss Recovery) appliance.