Database Reference
In-Depth Information
Determine Adapter Count and Disk Layout
Once the performance requirements have been gathered, the next step is to determine the
virtual machine layout. How many PVSCSI adapters is this virtual machine going to
use? Remember, the more paths back to the storage array, the more options you provide
the operating system to send I/O out to the array. However, just because you can add
four PVSCI adapters, does not mean that you should. If you have a database that is
housing configuration information for an application, does it need four PVSCSI adapters
and the VMDK files fanned out across all these controllers? Probably not. Balance
performance requirements with management overhead. Again, this is where database
tiering can assist.
VMDK versus RDM
In terms of choosing VMDK files or RDM, the guidance we provide is to choose
VMDK files unless you have a specific requirement that will drive you to choosing
RDMs. Choosing VMDK files and building your virtual machines with VMDK files is
on par from a performance perspective with RDMs, so performance capabilities should
not be taken into consideration. In addition, going with VMDKs is a way to future-proof
your implementation. As VMware introduces new features, functions, and capabilities
to the storage stack, your virtual machines will be able to benefit from these new
features. What are the reasons to choose RDM? The main driver is the decision point to
use Microsoft Windows AlwaysOn Failover Cluster Instance. VMware requires that
RDMs be used as part of this configuration. The other reasons customers will choose
RDMs is due to their backup methodology and tools, along with the requirement to
leverage SAN monitoring tools that function at the LUN level for granular detail around
performance. Our recommendation is to use VMDKs unless driven by architectural
reasons.
Note
To read more about VMDK versus RDM, read this blog article:
rdm.html
.
VMDK Provisioning Type
When provisioning a VMDK, the vSphere administrator has three options to choose
from: Thin Provision, Thick Provision Lazy Zeroed, and Thick Provision Eager Zeroed.
Before we get into the details around the VMDK provisioning type, we want to cover
VAAI (vStorage APIs for Array Integration) because this feature can have an impact on
the default behavior of the VMDK during provisioning time and implications to the
