vmlimitperhost client option
The vmlimitperhost option specifies the maximum number of virtual machines on an ESX server that can be included in a parallel backup operation.
- Preferred setting
- The preferred value is the default value of 0. By using the default value, you set no limits on
the maximum number of virtual machines on an ESX server that can be included in a parallel backup
operation. Verify that the value for the vmlimitperhost option is compatible
with the value for the vmmaxparallel option.
Set the vmlimitperhost option to the highest value that can still maintain a tolerable processor load on any single vSphere host for a virtual backup workload. Ensure that backup sessions are distributed equally across the affected vSphere hosts.
When you are specifying the setting, consider the set of virtual machines that are being backed up.
For example, if a set of 10 virtual machine guests is hosted on 5 vSphere hosts, and vmmaxparallel is set to 10, set the vmlimitperhost option to 2. In this way, you can distribute the parallel backup sessions across the hosts during a 10-guest parallel backup operation.
- Effects on performance
- The vmlimitperhost, vmmaxparallel, and
vmlimitperdatastore options limit the number of parallel backup operations that
occur overall and for any single vSphere host. You can use these options to reduce the processor
load that parallel backups can create on a vSphere host.
For a set of virtual machine guests that you back up, the order that IBM Storage Protect uses for creating backup sessions is random. Depending on the setting for the vmmaxparallel option, it might be possible that too many backup sessions would involve too few vSphere hosts at any one time during a backup operation.
The vmlimitperhost option can be used to ensure that no more than the number of backup sessions that are indicated by the vmlimitperhost option value affect any one host.
- Potential trade-offs for this setting
- Setting a value too low might artificially limit the maximum number of concurrent virtual
machine backups in an environment to less than what is feasible. However, a low value might be
necessary to throttle the amount of data that is sent to the IBM
Storage Protect server, or to reduce the processor load on the
involved vSphere hosts.
Setting a value too high might result in elevated processor loads on certain vSphere hosts.