Server switchover is a feature that allows the user to switch over applications from a primary server to a predefined spare server when the primary server fails or is stopped for maintenance.
It can also perform Auto-Recovery, which automatically switches applications over to a spare server when a hardware failure is detected on the primary server.
Server switchover can be realized through three different methods, as described below. The switchover method used by a given server is automatically selected when configuring its recovery settings. If HBA address rename settings were already made when applying recovery settings, the HBA address rename method will be automatically selected. Similarly, the VIOM profile exchange method is automatically selected if a server profile was already assigned to the server in VIOM.
However, each method has its own restrictions regarding the supported hardware environment. For details, refer to the corresponding "Note" in "1.2 Hardware Environment" of the "ServerView Resource Coordinator VE Installation Guide".
Backup and restore method
In a local boot environment, this method restores a system image backup to a spare server, which is then automatically started up.
This is selected under the following cases.
When a virtual WWN or boot configuration have not been set via the HBA address rename or VIOM server profile assigned to the primary server.
Select the "Local disk boot and SAN Data (back up and restore method)" checkbox when setting the spare server.
When HBA address rename or VIOM has been used to set a server profile for a server, the WWN and server profile also can be switched at server switchback.
After switchover, the operating system and its applications will resume on the spare server from the status they were in at the last system image backup.
However, since additional disks (disks used as data disks), are not subject to backup and restore, their content cannot be made accessible to the spare server with a server switchover.
However, since additional disks (disks used as data disks), are not subject to backup and restore, their content cannot be made accessible to the spare server with a server switchover.
When using more than one local disk, backup and restore of such additional data disks should be performed using external backup software.
However, when there are multiple sections on the first disk (Windows drives or Linux partitions), all sections become the target of backup and restore.
HBA address rename method
In a SAN boot environment, this method sets the WWN of a spare server's HBA to the same value as that originally set on the primary server. This allows the spare server to connect to and boot from the same boot disk that was used by the primary server. This method is used when HBA address rename settings have been made on the primary server. Because this method automatically starts the spare server from the primary server's boot disk, applications can be resumed without users being aware of the hardware replacement that occurred.
VIOM profile exchange method
This method is used in SAN boot environments where servers start from boot disks located in storage arrays. If the primary server fails, the WWN, MAC address, boot configuration, and network configuration set in its server profile are inherited by the spare server, which then automatically starts up from the same SAN disk. This method is used when a virtual WWN has been set via the VIOM server profile assigned to the primary server. Because this method automatically starts the spare server from the primary server's boot disk, applications can be resumed without users being aware of the hardware replacement that occurred.
The HBA address rename and VIOM profile exchange methods are also referred to as I/O virtualization methods.
For PRIMERGY BX servers, the network configuration (VLAN IDs of adjacent LAN switch ports) of the primary server will be inherited by the spare server. This is true for all methods of server recovery.
When using the VIOM server profile exchange or the backup and restore method, if a MAC address, boot configuration, or network configuration were assigned to the server (in its VIOM server profile), these settings will also be inherited by the spare server. Therefore, it is no longer necessary to re-configure applications or network devices that depend on MAC address values.
After two servers have been switched over, a failback operation can switch them back to their original configuration using the same switchover method. Conversely, server takeover is the operation that appoints the activated spare server as the new primary server instead of switching back servers to their original configuration.
Note
The backup and restore, and HBA address rename methods are not available if ServerView Deployment Manager is used on the admin LAN. Refer to "Appendix H Co-Existence with ServerView Deployment Manager" for details.
Auto-Recovery occurs when a hardware failure is detected. However, it does not occur when the operating system has stopped as a result of a software error or when the operating system is automatically rebooted.
Refer to "9.3 Server Switchover Conditions" for details on server switchovers.
Furthermore, since the Auto-Recovery is driven by a hardware failure, it prioritizes a fast recovery to a spare server instead of collecting an OS memory dump (which would be used to troubleshoot an OS failure).
Thus, even if a memory dump was set to be collected in the event of an OS failure, server recovery will take precedence and the memory dump will not be collected.
Server switchover can be realized by one of the following methods: Backup and restore method, HBA address rename method, or VIOM profile exchange method.
When configuring the HBA address rename function as the switchover method, first confirm that the HBA address rename settings have been configured properly before configuring the server switchover settings.
When server switchover is conducted using a Hyper-V VM host, prepare more than two physical NICs.
The network which VM hosts, such as the admin LAN for VM hosts, use to communicate with external servers should be dedicated only to physical servers, and not be configured for virtual networks.
In a network environment that has external virtual networks configured, disable all virtual networks for VM hosts. For details, refer to "A.2 Configuration Requirements".
It is not possible to specify spare servers for individual VM guests. It is either possible to store VM guests on a SAN or NAS shared disk and assign a spare server to the VM host, or use the VM high-availability feature provided by the server virtualization software used.
For details on the different high-availability features available in each server virtualization product, refer to "A.3 Functional Differences between Products".
For individual VM hosts, server switchover can be realized either from Resource Coordinator VE or from the high-availability feature provided with the server virtualization software used.
When primary and spare servers are placed in different chassis, and both servers are connected to PRIMERGY BX900 LAN switch blades operating in IBP mode, server switchover only works if the same port group names have been set on both LAN switch blades.
When using Intel PROSet for LAN redundancy, the switchover destination server may inherit the same MAC address as that of the source server, as Intel PROSet keeps an internal definition of MAC addresses. When using Intel PROSet for LAN redundancy, the switchover destination server may inherit the same MAC address as that of the source server, as Intel PROSet keeps an internal definition of MAC addresses. To avoid communication issues caused by MAC address conflicts, please be sure to re-configure MAC addresses on the destination server following a server switchover.
In environments where there are servers running physical OS's and servers with VM hosts and VM guests, if they both use HBA address rename or VIOM, by combining the following settings it is possible for a physical OS and a VM guest to share a spare server.
For details, refer to "Figure 9.3 Sharing a spare server between physical OS's and VM guests" in "9.2 Configuration".
Specify a VM host that does not run any VM guests as the spare server used to recover VM guests within the high-availability feature of the server virtualization software used.
Once the above settings have been made, a server failure will trigger the following recovery operations.
If the failed server was running a physical OS, Resource Coordinator VE will shut down the VM host on the spare server and switch the failed physical OS over to the spare server. If the failed server was a VM host running VM guests, the high-availability feature provided with the server virtualization software will recover the VM guests on the spare VM host server. Since physical OS's and VM guests share a common spare server, the two types of recovery described above can perform together: once one type of recovery occurs on a spare server, the other type of recovery can no longer be performed on that same spare server.
Information
Server switchover based on backup and restore takes approximately 3 minutes, plus the time required to restore the system image. Image restoration time depends on different factors such as disk space and network usage, but as an estimate, a disk of 73GB will take 30 to 40 minutes (the transfer of the system images takes between 10 to 20 minutes, while system restarts and other configuration changes take another 20 minutes).
Server switchover based on HBA address rename takes approximately 5 minutes, plus the time required to start up the original operating system and services on the spare server. If a VM host was running on the spare server, the time required to shutdown the spare server must also be included.
