5.5

Table Of Contents
Scalability Problems when Replicating Many Virtual Machines with
a Short RPO to a Shared VMFS Datastore on ESXi Server 5.0
Performance might be slow if you replicate a large number of virtual machines with a short Recovery
Point Objective (RPO) to a single virtual machine file store (VMFS) datastore that is accessible by
multiple hosts on the recovery site.
Problem
This problem occurs when running ESXi Server 5.0 on the recovery site. It can result in missed RPO
targets.
The number of virtual machines that can successfully replicate to a single, shared VMFS datastore
increases if the RPO targets are longer.
Follow the guidelines when calculating the number of virtual machines that you should replicate to a
single VMFS volume on the recovery site.
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If all your virtual machines have an RPO of 15 minutes, performance is affected when replicating 50
to 100 virtual machines to the same VMFS datastore.
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If all your virtual machines have an RPO of 30 minutes, performance is affected when replicating 100
to 200 virtual machines to the same VMFS datastore.
If you have heterogeneous RPO targets in a protection group, calculate the harmonic mean of the RPO
targets when calculating the number of virtual machines that you can replicate to a single VMFS volume.
For example, if you have 100 virtual machines with an RPO of 20 minutes and 50 virtual machines with
an RPO of 600 minutes, you calculate the harmonic mean of the RPO as follows:
150/(100/20 + 50/600) = ~30
In this example, the configuration is similar to a setup with 150 virtual machines, each having an RPO of
approximately 30 minutes. In this case, performance is affected if these 150 virtual machines replicate to
a single VMFS volume.
Cause
This problem affects only VMFS datastores that are shared by multiple hosts. It does not occur on
datastores that are local to one host or on other datastore types, such as NFS. This problem affects only
installations that are running ESXi Server 5.0.
The number of vSphere Replication servers is not relevant. These limits apply to the number of virtual
machines that you can replicate to a single VMFS datastore.
Solution
1 Upgrade ESXi Server to version 5.1 or later on the recovery site.
VMware vSphere Replication Administration
VMware, Inc. 84