Virtual server environments are replacing physical environments, as they bring cost benefits to the business, along with advantages such as better manageability, scalability and optimal utilization of resources. Resources can be allocated or de-allocated on the fly without downtime requirements, whether it's memory, CPU or storage. However, system administrators do encounter performance
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issues
in virtual server environments, largely due to storage performance issues. To avoid such server
virtualization and storage provisioning related bottlenecks, you should stress on these
aspects:
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· The foremost important thing that you
should stress on while provisioning
storage for server virtualization environments is throughput capability—and not just storage
capacity.
· Categorize virtual servers according to the applications that these
virtual machines will host, as applications have varying requirements.
· Pooling of storage resources makes management simple, and optimizes
resource utilization. However, it can lead to scarcity of resources for IO intensive applications.
So as a best practice in case of storage provisioning for VMWare, consider placing IO intensive
virtual disks on dedicated VMFS volumes or RDM, will yield good results. This server
virtualization and storage provisioning best practice ensures that heavily utilized virtual
servers don't access the same VMFS volumes, which may lead to a race condition.
· While provisioning
storage for server virtualization setups, RAID group should be chosen according to the desired
level of protection, performance and application requirements.
· Use RAID 3 for backup to disk applications, as it's the best option for
sequential workloads—sequential read and write performance. But do keep in mind that a RAID 3 drive
creates bottlenecks for random reads and writes.
· In general, RAID 5 should be preferred over RAID 3 (except in above
mentioned requirements). So for database applications with modest IOPS requirements, provision the
virtual machine using VMFS with underlying RAID 5 protection. RAID 5 groups should be configured in
combinations of 4+1 or 8 +1.
· For applications with high IOPS requirements, thevirtual
servers hosting those applications should be provisioned with VMFS or RDM having an underlying
RAID 1+0 protection, as it's the best candidate for transaction intensive workloads.
· When it comes to server
virtualization related storage provisioning, there are some parameters to be set for the HBA
that have a real time effect on storage performance—consult respective vendor manuals to optimize
them. These parameters are queue depth and execution throttle. Queue depth controls data allowed to
be on the storage network from that card. The default value is 32 for queue depth, which is good
for almost all the servers, and prevents the SAN congestion. However, we can tune it for
applications that are I/O intensive, and gain considerable performance enhancement by increasing
queue depth.
· If you are not certain about future requirements for a particular number
of virtual machines, use virtual provisioning features (offered by almost every vendor). So you can
allocate space from a storage pool to set the initial storage capacity that you want to
allocate—give the host an illusion of virtually allocated storage. So the servers contend for
storage from the virtual as the need grows. So you need not be worried about future requirements,
as thevirtual
servers dynamically get storage provisioning on a need basis.
| Anuj Sharma | |
About the author: Anuj Sharma is an EMC Certified and NetApp
accredited professional. Sharma has experience in handling implementation projects related to SAN,
NAS and BURA. He also has to his credit several research papers published globally on SAN and BURA
technologies.
This was first published in May 2010