December 18, 2012 | Written by: Bhanu Tholeti
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SmartCloud Enterprise+, also known as SCE+, is IBM’s private, hybrid cloud offering. It has all the capabilities to host and run production class workloads on virtual machines (VMs) provisioned with high availability (HA) features guided by the service level agreement (SLA).
What SLA options are available in SCE+?
There are four types of SLA options available for a customer to choose for a virtual machine while making a request:
How does SLA define high availability?
High availability configuration for virtual machines in SCE+ is directly proportional to the SLA a customer has selected for his virtual machine while provisioning.
For example: a Platinum SLA virtual machine has the highest-priority setting for restart, with minimal timeouts in error situations. Gold, Silver, and Bronze have decreasing restart priorities and longer timeouts in error situations.
The VMware vSphere High Availability (VMware HA) feature in IBM SmartCloud Enterprise+ enables automatic HA configuration for VMs provisioned on IBM System x. Its two key features are restart priority and heartbeat.
VM restart priority values resolve resource contention. The priority determines the preference that VMware HA gives to a VM if sufficient capacity is not available to power on all failed VMs. High-priority VMs on a host get preference over low-priority VMs.
The valid parameters for a single VM HA configuration are disable, high, medium and low.
Heartbeat time interval
The VMware VM health-monitoring feature in IBM SmartCloud Enterprise+ always checks for the response on a VM’s heartbeat services, which run in the VMware tools on every VM on a given host. If the heartbeat service is unable to respond to the health-monitoring service within a configurable timeout interval, the VM is a failed VM, and the corresponding reset action will be performed.
The lower the value of a heartbeat timeout interval, the faster the VM reboots. Heartbeat time interval is minimal for Platinum SLA, followed by Gold, Silver and Bronze.
Table 1 shows the restart-priority and heartbeat values configured for each SLA level:
*IBM recommends these values. Vendors, cloud administrators, or users can adjust the timeout intervals, depending on the prevailing environment and workload conditions.
In addition to the settings in Table 1, Platinum VMs are allocated storage in the mirrored datastores, which provides continuous availability of the VMs even in the event of storage-devices failure.
The implementation details for the above said features can be referenced in the article HA and SystemX in SCEp.
Stay tuned for Part 2 of my blog post for information on SystemP.