The first name format is the Extended Unique Identifier (EUI). iSCSI supports two name formats as well as aliases. ISCSI nodes have globally unique names that do not change when Ethernet adapters or IP addresses change. These will be examined in the next section. Several identifiers exist in iSCSI to make this happen, including iSCSI Name, ISID (iSCSI session identifiers), TSID (target session identifier), CID (iSCSI connection identifier), and iSCSI portals.
Similarly, iSCSI targets must manage multiple, parallel communications links to multiple initiators. ISCSI initiators must manage multiple, parallel communication links to multiple targets. For example, VMware vCenter™ Site Recovery Manager™ may build upon iSCSI asynchronous storage replication for simple, reliable site disaster protection. Asynchronous replication, which is not dependent upon latency sensitivity, makes iSCSI an ideal solution. Latency introductions bring greater delays to data transfers and might impact application performance. For synchronous replication writes (in the case of high availability) or remote data writes, iSCSI might not be a good fit. It has prevalently been approached as a local area network technology. ISCSI was considered a technology that did not work well over most shared wide-area networks. Most enterprise-level networking chipsets today offer TCP offload or checksum offload, which vastly improves CPU overhead. TOEs shift TCP packet processing tasks from the server CPU to specialized TCP processors on the network adaptor or storage device. One way of overcoming this demand for CPU resources is to use a feature called a TOE (TCP/IP offload engine). These interfaces tend to consume a significant amount of CPU Resource.
#MD3220I VMWARE 6.0 IO CHARACTERISTICS TYPE SOFTWARE#
When implementing software iSCSI that uses network interface cards rather than dedicated iSCSI adapters, gigabit Ethernet interfaces are required. There are other mechanisms such as port aggregation and bonding links that deliver greater network bandwidth. Network bandwidth is dependent on the Ethernet standards used (1Gb or 10Gb). For more details on this issue please refer to: Īnother consideration is the network bandwidth. VMware recommends consulting the iSCSI array vendor for specific recommendations around DelayedAck. Various iSCSI array vendors even recommend disabling DelayedAck for iSCSI adapter. Although some iSCSI storage vendors have implemented Delayed Ack and Congestion Avoidance as part of their TCP/IP stack, not all have. There can be multiple reasons for an iSCSI path being overloaded, ranging from oversubscription (too much traffic), to network switches that have a low port buffer. When a network path carrying iSCSI storage traffic is substantially oversubscribed, a bad situation quickly grows worse and performance further degrades as dropped packets must be resent. FC communication over a dedicated path has a built-in pause mechanism when congestion occurs. When an iSCSI path is overloaded, the TCP/IP protocol drops packets and requires them to be resent. One major difference between iSCSI and FC relates to I/O congestion.
These factors contribute to lower-cost implementations. In comparison to FC and Fibre Channel over Ethernet (FCoE) SAN deployments, iSCSI requires less hardware, it uses lower-cost hardware, and more IT staff members might be familiar with the technology. It is comparatively inexpensive and it is based on familiar SCSI and TCP/IP standards. These can be consumed in the same way as any other block storage device.įor datacenters with centralized storage, iSCSI offers customers many benefits. Block devices are presented across an IP network to your local system. Unlike NAS, which presents devices at the file level, iSCSI makes block devices available via the network. As with SCSI over Fibre Channel (FC), iSCSI presents SCSI targets and devices to iSCSI initiators (requesters). ISCSI is a protocol that uses the TCP/IP to transport SCSI commands, enabling the use of the existing TCP/IP networking infrastructure as a SAN. Read-Only File Systems on Linux Guest OS.All Paths Down and Permanent Device Loss.Installing a vSphere Host on an iSCSI LUN.Compatible Network Interface Card (NIC).Booting a vSphere Host from Software iSCSI.Sizing Considerations - Recommended Volume Size.Software iSCSI Multipathing Configuration Steps.iSCSI Multipathing via Port Binding for Availability.Availability Options – Multipathing or NIC Teaming.
Best Practices For Running VMware vSphere On iSCSI
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