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Volume mapping layout
42 Dell EMC SC Series: Best Practices with VMware vSphere | 2060-M-BP-V
9 Volume mapping layout
In addition to volume sizing, another important factor to consider is the placement of files and virtual machine
data.
9.1 Multiple virtual machines per volume
One of the most common techniques in virtualization is to place more than one virtual machine on each
volume. Encapsulation of virtual machines within datastores results in higher consolidation ratios. When
deciding how to lay out the VMFS volumes and virtual disks, it should reflect the performance and backup
needs of the guest operating systems. Regardless of the layout of the virtual machines, there are some basic
concepts that should be considered.
9.1.1 Storage of non-virtual machine files
One general recommendation is to create a content library or a datastore for administrative items to store
virtual machine templates, ISO images, virtual floppies, or scripts.
9.1.2 Separation of operating system page files
In situations where memory swapping cannot be avoided, one technique to consider with virtual machine
placement is separating the operating system paging files or swap files onto a separate datastore.
There are two main reasons for separating operating system page files onto their own datastore. First,
because page files can generate a lot of disk activity, this practice could keep volume snapshots (replays)
smaller. Second, if replicating those volumes, this practice will conserve bandwidth by not replicating the
operating system page file data.
Depending on the memory-swap conditions unique to each environment, separating page files may or may
not make a significant reduction in snapshot sizes. A good way to determine whether separating page files
will make a difference is to use the vSphere client performance charts to monitor swap or balloon usage of the
ESXi host. If these numbers are high, consider testing the separation of page files to determine the impact.
If separating page files will make an impact in reducing snapshot sizes, the general recommendation is to
create pairs of volumes for each datastore containing virtual machines. If a volume is created to contain 10
virtual machines, then a second volume should be created to store the operating system page files for those
10 machines. For example:
Create one datastore for virtual machines: This datastore will usually contain the virtual machine disk
(VMDK) files, configuration files, and logs for the virtual machines.
Create one paired datastore for the corresponding virtual machine page files: This datastore should
contain virtual machine page files. Using Windows as an example, create a virtual disk (P:) on this volume
large enough to store the Windows paging file for each virtual machine. This volume can be sized
considerably smaller than the main datastore since it only needs enough space to store page files.
A question often asked is: Should all operating system page files be placed on a single datastore? This
practice is not a good idea for the following reasons.
First, the page file datastore can also experience contention from queue depth utilization or disk I/O. Too
many VMDK files during a sudden memory-swapping event could decrease performance even further. For
example, if a node in the ESXi HA cluster fails and the affected virtual machines are consolidated on the