vSphere Storage - ESXi 5.1 - Documentation - VMware

vSphere Storage
If there are no running virtual machines on the VMFS datastore, after you change the ID of the LUN, you
must use rescan to reset the ID on your host. For information on using rescan, see “Storage Refresh and
Rescan Operations,” on page 135.
n If you need to change the default iSCSI name of your iSCSI adapter, make sure the name you enter is
worldwide unique and properly formatted. To avoid storage access problems, never assign the same iSCSI
name to different adapters, even on different hosts.
Optimizing iSCSI SAN Storage Performance
Several factors contribute to optimizing a typical SAN environment.
If the network environment is properly configured, the iSCSI components provide adequate throughput and
low enough latency for iSCSI initiators and targets. If the network is congested and links, switches or routers
are saturated, iSCSI performance suffers and might not be adequate for ESXi environments.
Storage System Performance
Storage system performance is one of the major factors contributing to the performance of the entire iSCSI
environment.
If issues occur with storage system performance, consult your storage system vendor’s documentation for any
relevant information.
When you assign LUNs, remember that you can access each shared LUN through a number of hosts, and that
a number of virtual machines can run on each host. One LUN used by the ESXi host can service I/O from many
different applications running on different operating systems. Because of this diverse workload, the RAID
group that contains the ESXi LUNs should not include LUNs that other hosts use that are not running ESXi
for I/O intensive applications.
Enable read caching and write caching.
Load balancing is the process of spreading server I/O requests across all available SPs and their associated host
server paths. The goal is to optimize performance in terms of throughput (I/O per second, megabytes per
second, or response times).
SAN storage systems require continual redesign and tuning to ensure that I/O is load balanced across all storage
system paths. To meet this requirement, distribute the paths to the LUNs among all the SPs to provide optimal
load balancing. Close monitoring indicates when it is necessary to manually rebalance the LUN distribution.
Tuning statically balanced storage systems is a matter of monitoring the specific performance statistics (such
as I/O operations per second, blocks per second, and response time) and distributing the LUN workload to
spread the workload across all the SPs.
Server Performance with iSCSI
You must consider several factors to ensure optimal server performance.
Each server application must have access to its designated storage with the following conditions:
n High I/O rate (number of I/O operations per second)
n High throughput (megabytes per second)
n Minimal latency (response times)
128 VMware, Inc.