Your First System i (AS400) High Availability Role Swap WILL FAIL
The Case for System Assurance Planning and Testing
Before we sell them High Availability and Business Continuity systems we tell our clients that their first role swap will fail. Our competitors think we're crazy to do that. But we want our customers to know the truth so they plan and test before a critical role swap occurs - so that the first critical role swap IS successful.
You see, for a successful role swap, it's not about the IBM System i hardware or the HA software, both of which are extraordinarily reliable. Unfortunately, the attention is too often focused on the hardware, the software and the software integration.
Instead, what should be the focus of the attention is your network. Quite simply, if you network is improperly set up, your role swap will always fail. Guaranteed.
To facilitate a successful role swap, you should have a virtual LAN - or VLAN - so that when you role swap your users from the production server to the backup target server, the cutover is transparent. When a VLAN is properly set up, you can cut over in under 5 minutes. We have clients - with over 1,000 users - who role swap in under 5 minutes!
During our typical HA solution assurance review with our clients, we uncover the fact that they have static IP network addressing - the most common cause of role swap failure.
- A static IP address is a unique address for a specific computer. In a disaster or role swap, a specific IP address may not be addressable, or it may require the network administrator to reassign every user's IP address. This is VERY TIME-CONSUMING.
- In contrast, a virtual IP, or dynamic IP, is not connected to a specific computer or network interface card (NIC) on a computer. Incoming packets are sent to the VIP address but all packets travel through real network interfaces.
- Virtual IPs are mostly used for connection redundancy; a VIP address may still be available if a computer or NIC fails because an alternative computer or NIC replies to connections. Dynamic IP Addresses are most frequently assigned on LANs and broadband networks by Dynamic Host Configuration Protocol (DHCP) servers. They are used because it avoids the administrative burden of assigning specific static addresses to each device on a network.
- Most of our clients confess that their production networks are set up with static IP addresses and that they need help to convert to virtual IP there as well as for their target location.
As part of HA planning, setup and testing, we explain to our clients the importance of a VLAN and how to make the change from a static to a virtual environment. Then, when we are onsite and test for the role swap, we can flush out the remaining "bugs" in the VLAN, resulting in a perfect role swamp.
We have discovered - by experience - that this precautionary attention to the network is the best way to make sure a role swap will not fail during a crisis.
To your success!