When enabling datastore maintenance mode, Storage DRS will move virtual machines out of the datastore as fast as it can. The number of virtual machines that can be migrated in or out of a datastore is 8. This is related to the concurrent migration limits of hosts, network and datastores. To manage and limit the number of concurrent migrations, either by vMotion or Storage vMotion, a cost and limit factor is applied. Although the term limit is used, a better description of limit is maximum cost.

In order for a migration operation to be able to start, the cost cannot exceed the max cost (limit). A vMotion and Storage vMotion are considered operations. The ESXi host, network and datastore are considered resources. A resource has both a max cost and an in-use cost. When an operation is started, the in-use cost and the new operation cost cannot exceed the max cost.



The operation cost of a storage vMotion on a host is “4”, the max cost of a host is “8”. If one Storage vMotion operation is running, the in-use cost of the host resource is “4”, allowing one more Storage vMotion process to start without exceeding the host limit.

As a storage vMotion operation also hits the storage resource cost, the max cost and

in-use cost of the datastore needs to be factored in as well. The operation cost of a Storage vMotion for datastores is set to 16, the max cost of a datastore is 128. This means that 8 concurrent Storage vMotion operations can be executed on a datastore. These operations can be started on multiple hosts, not more than 2 storage vMotion from the same host due to the max cost of a Storage vMotion operation on the host level.



< config >

< vpxd >

< ResourceManager >

< MaxCostPerEsx41Ds > new value < /MaxCostPerEsx41Ds >

< /ResourceManager >

< /vpxd >

< /config >

To throttle the number of storage vMotion operations to reduce the IO hit on a datastore during maintenance mode, it preferable to reduce the max cost for provisioning operations to the datastore. Adjusting host costs is strongly discouraged. Host costs are defined as they are due to host resource limitation issues, adjusting host costs can impact other host functionality, unrelated to vMotion or Storage vMotion processes.Adjusting the max cost per datastore can be done by editing the vpxd.cfg or via the advanced settings of the vCenter Server Settings in the administration view.If done via the vpxd.cfg, the value vpxd.ResourceManager.MaxCostPerEsx41Ds is added as follows: