In 2011 many small-medium-sized businesses will be taking their first steps towards virtualising their IT estate in order to reduce costs and improve flexibility. This is no surprise as VMware is putting a great deal of focus on this market by reducing the price and increasing the functionality of the "entry level" Essentials and Essentials plus bundles.
One of the new features now available in the VMware VSphere Essentials Plus kitbag is the inclusion of vMotion giving the ability to migrate virtual machines from one physical host to another with no downtime.
A pre-requisite for the use of vMotion is shared storage such as a NAS or a SAN. If a SAN will be the preferred option , there is a decision to be made, iSCSI or Fibre Channel storage.
An iSCSI SAN is now a very popular option that should be considered for providing this shared storage in a VMware environment.
iSCSI is typically cheaper to implement than Fibre Channel (FC) storage and can now start to compete on performance with the emergence of 10Gb Ethernet. For me there is also the advantage of a reduced cost of ownership as iSCSI uses much the same hardware (Ethernet switches) and protocols (TCP/IP) that many IT professionals are already familiar with making implementation and troubleshooting simpler.
If you are looking to deploy iSCSI storage in a VMware environment, below are some high level guidelines that I would recommend are followed:
- Keep iSCSI storage traffic on its own dedicated network. Putting SAN traffic on an already busy LAN will pretty much kill your network performance and avoid routing at all costs. If you must use the same switching infrastructure for general and iSCSI traffic, make sure that you implement VLAN's to separate this traffic.
- Split your SAN storage across as many spindles as you can in order to be able to cope with increased storage throughput demands
- Use multiple physical NIC's for the vSwitch that will provide iSCSI connectivity to provide redundancy as only one iSCSI initiator can be configured on each ESX host. For additional resilience, each physical NIC should be connected to a separate switch.
- If available on your switch, consider the use of Jumbo Frames but bear in mind that only specific workloads will benefit. I would recommend running performance testing in your environment with these turned on then off to see how much difference this makes
- Use the new PVSCSI (Para virtual SCSI) adapter rather than the standard LSI or BusLogic adapters. PVSCSI adapters are high-performance storage adapters that can result in greater throughput and lower CPU utilization. PVSCSI adapters are best suited for environments, especially SAN environments, where hardware or applications drive a very high amount of I/O throughput
