Database Reference
In-Depth Information
Table 6.3
Supported Virtual Machine Storage IO Controllers
Each virtual SCSI controller (vSCSI) allows up to 15 disks to be connected, for a total
of 60 vSCSI disks per virtual machine. With hardware version 10 in ESXi 5.5, VMware
has introduced a new SATA (AHCI) controller. Each SATA controller allows up to 30
disks to be connected, for a total of 120 vSATA disks per virtual machine. vSCSI and
vSATA can be combined on the same virtual machine for a maximum of 180 virtual
disks per VM.
BusLogic and LSI Parallel are legacy controllers not suitable for SQL Server 2012
virtual machines. If you are virtualizing on ESXi 5.5 and using virtual hardware version
10, SATA may have some use if you have a need for a particularly large number of
virtual disks per VM. However, for almost all cases, you will choose either LSI Logic
SAS or VMware PVSCI (Paravirtualized SCSI). The reason why will become clear as
we look in more detail at each of these controllers.
Choosing the Right Virtual Storage Controller
A virtual storage controller is very much like a physical storage controller in terms of
how Windows interacts with it. Choosing the right virtual storage controller can have a
big impact on your performance. In this section, we cover the different controller
options and the performance characteristics of each type. This will help you make the
right virtual storage controller choice based on your requirements and constraints.
Remember back to Principle 1: Your database is just an extension of your storage? Our
goal is to maximize the parallelism of IOs from SQL Server and Windows through to the
underlying storage devices. We don't want IOs to get held up unnecessarily in Windows
itself. However, care needs to be taken because we don't want to issue so many IOs that
the backend storage devices get overloaded and cause additional latency. Overloading
your backend storage will not just impact SQL Server, but could also impact all of your
other VMs. We will discuss later how you can use features of VMware vSphere to
ensure quality of service to your critical databases and other virtual machines to protect
