Virtual Server Agent (VSA) hypervisors use a common framework to distribute backup jobs, as described in Backup Workload Distribution.
This topic describes considerations that are specific to Red Hat Virtualization.
To adjust the default behavior, see Performance Tuning for Backups.
Dispatch Logic
Virtual machine backup jobs are allocated to VSA proxies according to the following priorities:
-
Each VSA proxy manages backups for virtual machines hosted on the same Red Hat data center.
-
When multiple VSA proxies are available for a cluster, the round-robin method is used to choose the least loaded proxy.
-
If none of the other criteria can be used to allocate jobs for a VM, jobs are allocated by default to the coordinator node. If the coordinator node cannot access the cluster for the VM disks, the job fails.
If only one proxy is available to back up a VM, the VM is statically assigned to that proxy.
Proxy Selection
The virtualization client enables automatic load balancing of backup jobs across multiple VSA proxies.
The CommServe system attempts to contact the coordinator node (the first in the list of proxies). If the coordinator node is not available, the system tries the next proxy in the list until finding an available proxy. Once a proxy is successfully contacted, it acts as the coordinator for the remainder of the job. The coordinator proxy contacts the remaining proxies in the list. Any proxies that are not available are not used for the current job attempt.
Once all proxies to be used for the job are known, the coordinator distributes the virtual machines among the available proxies. The decision of which proxy to use for a given virtual machine is based on the best path for backing up that virtual machine:
-
Virtual machines are backed up by proxies that are running as virtual machines on the same host.
-
Virtual machines are backed up by proxies that are running as virtual machines on hosts that have access to the datastore.
-
Virtual machines are backed up by proxies that are on the same subnet as the virtual machine’s host.
-
The remaining virtual machines are distributed evenly across the proxies.
If one of the proxies becomes unavailable during the backup, the virtual machines allocated to that proxy are distributed among the remaining proxies. If the proxy becomes available again while the same backup job is running, it is not used for backups unless you suspend the backup job and resume it again.