vmlimitperdatastore client option
The vmlimitperdatastore option specifies the maximum number of virtual machines in a data store that can be included in a parallel backup operation.
- Preferred setting
- The preferred value is the default value of 0. By using this value, you set no limit on the
maximum number of virtual machines in a data store that can be included in a parallel backup
operation. However, ensure that the selected value is compatible with the value that is being used
for the vmmaxparallel option.
Set the vmlimitperdatastore option to the highest value that can still maintain a tolerable processor load on any single vSphere host for a virtual machine backup workload. In addition, adjust this value so that the backup workload is spread across as many vSphere data stores as possible.
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 data stores, and vmmaxparallel is set to 10, set the vmlimitperdatastore option to 2. In this way, you can distribute the parallel backup sessions across the data stores during a 10-guest parallel backup operation.
- Effects on performance
- The vmlimitperdatastore, vmmaxparallel, and
vmlimitperhost options limit the number of parallel backups that occur overall
and for any single vSphere datastore. You can set these options to reduce the processor load that
parallel backups can create on a vSphere host or hot spots on vSphere datastore LUNs.
For a set of virtual machine guests that you back up, the order that IBM Storage Protect uses to create 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 datastores.
The vmlimitperdatastore option can be used to ensure that no more than the number of backup sessions that are indicated by the vmlimitperdatastore option affect any one datastore.
- 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
vSphere hosts or the I/O load on vSphere data stores.
Setting a value too high might result in elevated processor loads on certain vSphere hosts, depending on the mapping of VMware data stores to hosts. Setting too high a value might also result in elevated loads on certain vSphere data stores. This outcome might lead to inefficiencies because the underlying LUNs of those data stores must handle excessive I/O processes compared to others.