vSphere Storage - ESXi 5.1 - Documentation - VMware
vSphere Storage - ESXi 5.1 - Documentation - VMware
vSphere Storage - ESXi 5.1 - Documentation - VMware
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<strong>vSphere</strong> <strong>Storage</strong><br />
Figure 10-1. Target Compared to LUN Representations<br />
target<br />
LUN LUN LUN<br />
storage array<br />
target target target<br />
LUN LUN LUN<br />
storage array<br />
Three LUNs are available in each of these configurations. In the first case, the host detects one target but that<br />
target has three LUNs that can be used. Each of the LUNs represents individual storage volume. In the second<br />
case, the host detects three different targets, each having one LUN.<br />
Host-based iSCSI initiators establish connections to each target. <strong>Storage</strong> systems with a single target containing<br />
multiple LUNs have traffic to all the LUNs on a single connection. With a system that has three targets with<br />
one LUN each, a host uses separate connections to the three LUNs. This information is useful when you are<br />
trying to aggregate storage traffic on multiple connections from the host with multiple iSCSI HBAs, where<br />
traffic for one target can be set to a particular HBA, while traffic for another target can use a different HBA.<br />
iSCSI <strong>Storage</strong> System Types<br />
<strong>ESXi</strong> supports different storage systems and arrays.<br />
The types of storage that your host supports include active-active, active-passive, and ALUA-compliant.<br />
Active-active storage<br />
system<br />
Active-passive storage<br />
system<br />
Asymmetrical storage<br />
system<br />
Virtual port storage<br />
system<br />
Discovery, Authentication, and Access Control<br />
Allows access to the LUNs simultaneously through all the storage ports that<br />
are available without significant performance degradation. All the paths are<br />
active at all times, unless a path fails.<br />
A system in which one storage processor is actively providing access to a given<br />
LUN. The other processors act as backup for the LUN and can be actively<br />
providing access to other LUN I/O. I/O can be successfully sent only to an active<br />
port for a given LUN. If access through the active storage port fails, one of the<br />
passive storage processors can be activated by the servers accessing it.<br />
Supports Asymmetric Logical Unit Access (ALUA). ALUA-complaint storage<br />
systems provide different levels of access per port. ALUA allows hosts to<br />
determine the states of target ports and prioritize paths. The host uses some of<br />
the active paths as primary while others as secondary.<br />
Allows access to all available LUNs through a single virtual port. These are<br />
active-active storage devices, but hide their multiple connections though a<br />
single port. <strong>ESXi</strong> multipathing does not make multiple connections from a<br />
specific port to the storage by default. Some storage vendors supply session<br />
managers to establish and manage multiple connections to their storage. These<br />
storage systems handle port failover and connection balancing transparently.<br />
This is often referred to as transparent failover.<br />
You can use several mechanisms to discover your storage and to limit access to it.<br />
You must configure your host and the iSCSI storage system to support your storage access control policy.<br />
74 <strong>VMware</strong>, Inc.