A single Tivoli® Storage Manager data
mover node can be used to concurrently back up multiple virtual machines.
When the back ups are initiated, the client establishes parallel
sessions to copy the data to the Tivoli Storage Manager server.
For backing up VMware virtual machines, client options are provided
so you can optimize the backups so they do not adversely affect the
ESX servers that are hosting the virtual machines. The options are
described in detail in
Client options reference.
A short summary is provided here to illustrate their use.
- The vmmaxparallel option limits how many virtual
machines can be backed up at any one time.
- The vmlimitperhost option limits how many virtual
machines can be backed up, at any one time, per ESX server.
- The vmlimitperdatastore option limits how many
virtual machines can be backed up, at any one time, per datastore.
For backing up Hyper-V virtual
machines, the vmmaxparallel option limits how many
virtual machines can be backed up at any one time.
- vmmaxparallel
- The vmmaxparallel option specifies how many virtual
machines can be backed up at any one time. The optimal value for vmmaxparallel is not obvious; it depends on the processing
power of the vStorage server that the Tivoli Storage Manager data
mover node runs on, and the performance of I/O between the client
and the Tivoli Storage Manager server. For example, if you are moving data to the server
over a busy LAN, you might need to limit the number of virtual machines
in each parallel backup session. Similarly, if the vStorage server
processing capabilities are limited, for any reason, this is also
a reason to restrict the value for vmmaxparallel.
The default for this option is 1. Using the default value mimics the
same behavior of older clients, where only one virtual machine is
backed up during a session.
- vmlimitperhost
- The vmlimitperhost option specifies how many
virtual machines can be backed up from a single ESX/ESXi host, at
the same time. Like the value for vmmaxparallel,
you might have to experiment with this setting to find the optimum
value. On ESX/ESXi servers that are heavily used, you might need to
restrict the value for vmmlimitperhost so you do
not adversely affect the vSphere server performance. On servers that
are not as heavily used, you can include more virtual machines.
- vmlimitperdatastore
- The vmlimitperdatastore option limits the maximum
number of virtual machines that can be backed up, at any one time,
from a datastore. In a multiple datastore VMware environment, you
can use this option to reduce the burden that is placed on any one
datastore during a parallel backup operation.
These options work in concert with each other. Examples are provided
to illustrate how these options determine how many virtual machines
are backed up from any host or datastore.
Parallel backup examples
In the following
figures, the circled virtual machines are the virtual machines that
are selected for backup processing, which is based on the option settings
in domain.vmfull.
Example 1: Each VM is stored in a single datastore
Figure 1 shows that each of the circled virtual machines has its data
saved in a unique datastore. Assume that the parallel backup options
are set to the following values:
- vmmaxparallel 3
- vmlimitperhost 1
- vmlimitperdatastore 1
Figure 1. Virtual machines using unique datastores.
In Host A, only virtual machines 1 and 5 match the
selection criteria on a domain.vmfull statement.
In Host B, only virtual machine 2 matches the selection criteria.
In this configuration, each virtual machine has a separate datastore,
so the vmlimitperdatastore setting is valid. But,
since vmlimitperhost is set to one, only one virtual
machine (vm1 or vm5) from Host A and one virtual machine (vm2) from
Host B are included when the Backup VM operation is run; only two
virtual machines are included in this backup session.
Example 2: Same as example 1, but with a different
setting for vmlimitperhost
Figure 2 shows that each of the circled virtual machines has its data
saved in a unique datastore. In this configuration, the
vmlimitperhost is increased to two to illustrate how the option increase changes
the Backup VM operation. Assume that the parallel backup options are
now set to the following values:
- vmmaxparallel 3
- vmlimitperhost 2 (an increase of 1)
- vmlimitperdatastore 1
Figure 2. Virtual machines using
unique datastores, with different option value for vmlimitperhost.
The same virtual machines match the domain.vmfull criteria as they did in the previous example. However, with the
increase in the vmlimitperhost setting, now a total
of three virtual machines are included in a Backup VM operation (vm1
and vm5 from Host A, and vm2 from Host B).
Example 3: Some VMs share datastores
Figure 3 shows
that the VMDK and configuration files for virtual machine 5 in Host
A is stored in two datastores. To include both vm1 and vm5 in Host
A in the parallel backup operation, the value of vmlimitperdatastore must be increased to at least two. If vmlimitperdatastore is not increased to two, or higher, the backup of the second virtual
machine (vm5), in Host A, cannot be started until the first virtual
machine (vm1) backup is completed because the two VMs share data in
datastore1.
Figure 3. Virtual machines sharing
a datastore.