How to virtualise SQL Server

Generally, SQL installations on VMware aresimilar to that performed as they would be on physical hosts with additional optimisation performed on VMware.

I have been running SQL sever VMware since 2002 and even with the obvious benefits listed above performance has been my biggest gripe. The fact that processors, storage and its connections are generally shared means that I have kept the most demanding servers on separate high powered machines. That said, a lot of servers can be fully provisioned on high spec equipment running ESX.

There are some important areas to understand when considering moving onto VMware, chief among these are CPU, memory and disks.

For the purposes of this discussion I will be looking at the option available with VMWare's ESX server which I believe is the only viable option for a production SQL server

CPU
CPU virtualisation adds varying amounts of overhead, depending on a number of different factors. For processor-intensive applications like SQL server the CPU overhead of virtualisation is likely to result in a reduction in overall performance. However, this is mitigated to some degree by the efficient manner in which VMware balances processor loads and virtual machines running on VMware can leverage multi- cores and multi-processor configurations, making it possible to run processor-intensive workloads. VMware allows you to assign different virtual CPUs to your virtual servers.

Memory
Memory if the most common factor limiting the number of virtual machines you can run on a single physical machine IT does not reduce the memory demands of SQL or the windows operations system. VMware however, has limited memory overhead and its RAM over commitment allows better memory allocation and utilisation. IT can dynamically increase or reduce the amount of RAM assigned to a virtual machine as the application demands increase or reduce. This allows higher severe consolidation than is possible with static virtual memory.

Disks
VMware machines run complete operating systems and the stiorage requirements of SQL server need to be taken into consideration when deciding to move to a VMware infrastructure. SQL server is a I/O intensive application and the impact on disk I/O of simultaneous disk access by multiple virtual machines consolidated on a single physical server can result in performance degradation. VMware goes someway to improving I/O performance through VMFS. Centralised storage helps reduce latency and increase throughput

Disk Configuration Options
You can configure virtual machines with multiple virtual SCSI drives which appear to the virtual machine as a SCSI device attached to a SCSI adapter.