5.5

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.
n
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.
n
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.
2 If you cannot upgrade ESXi Server to version 5.1 or later, redistribute the replicated virtual machines or
adjust their RPO.
n
Reduce the number of virtual machines with a short RPO that replicate to a single VMFS volume,
for example by using a larger number of smaller datastores.
n
Increase the RPO of the virtual machines replicating to a single VMFS volume to create a longer
harmonic mean RPO.
Chapter 10 Troubleshooting SRM Administration
VMware, Inc. 119