vsphere-esxi-vcenter-server-55-storage-guide

vSphere StorageIf 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 Refreshand Rescan Operations,” on page 123.• If you need to change the default iSCSI name of your iSCSI adapter, make sure the name you enter isworldwide unique and properly formatted. To avoid storage access problems, never assign the sameiSCSI name to different adapters, even on different hosts.Optimizing iSCSI SAN Storage PerformanceSeveral factors contribute to optimizing a typical SAN environment.If the network environment is properly configured, the iSCSI components provide adequate throughput andlow enough latency for iSCSI initiators and targets. If the network is congested and links, switches or routersare saturated, iSCSI performance suffers and might not be adequate for ESXi environments.Storage System PerformanceStorage system performance is one of the major factors contributing to the performance of the entire iSCSIenvironment.If issues occur with storage system performance, consult your storage system vendor’s documentation forany relevant information.When you assign LUNs, remember that you can access each shared LUN through a number of hosts, andthat a number of virtual machines can run on each host. One LUN used by the ESXi host can service I/Ofrom 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 notrunning 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 associatedhost server paths. The goal is to optimize performance in terms of throughput (I/O per second, megabytesper second, or response times).SAN storage systems require continual redesign and tuning to ensure that I/O is load balanced across allstorage system paths. To meet this requirement, distribute the paths to the LUNs among all the SPs toprovide optimal load balancing. Close monitoring indicates when it is necessary to manually rebalance theLUN distribution.Tuning statically balanced storage systems is a matter of monitoring the specific performance statistics (suchas I/O operations per second, blocks per second, and response time) and distributing the LUN workload tospread the workload across all the SPs.Server Performance with iSCSIYou must consider several factors to ensure optimal server performance.Each server application must have access to its designated storage with the following conditions:• High I/O rate (number of I/O operations per second)• High throughput (megabytes per second)• Minimal latency (response times)116 VMware, Inc.