Information Technology Reference
In-Depth Information
number in the thousands, datastores that number in the hundreds, local and remote replicas
that number in the hundreds, and the highest possible workloads—all that perform consistently
even after component failures.
The most important considerations are as follows:
If you have a midrange array, recognize that it is possible to oversubscribe the storage pro-
cessors signii cantly. In such a situation, if a storage processor fails, performance will be
degraded. For some customers, that is acceptable because storage processor failure is rare.
For others, it is not, in which case you should limit the workload on either storage processor
to less than 50 percent or consider an enterprise array.
◆
Understand the failover behavior of your array. Active-active arrays use the i xed-path
selection policy by default, and active-passive arrays use the most recently used (MRU)
policy by default. (See the section “Reviewing Multipathing” for more information.)
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Do you need specii c advanced features? For example, if you want disaster recovery, make
sure your array has integrated support on the VMware vCenter Site Recovery Manager
HCL. Or, do you need array-integrated VMware snapshots? Do they have integrated man-
agement tools? More generally, do they support the vSphere Storage APIs? Ask your array
vendor to illustrate its VMware integration and the use cases it supports.
◆
We're now left with the last major area of storage fundamentals before we move on to dis-
cussing storage in a vSphere-specii c context. The last remaining area deals with choosing a
storage protocol.
Choosing a Storage Protocol
vSphere offers several shared storage protocol choices, including Fibre Channel, FCoE, iSCSI,
and Network File System (NFS), which is a form of NAS. A little understanding of each goes a
long way in designing the storage for your vSphere environment.
Reviewing Fibre Channel
SANs are most commonly associated with Fibre Channel storage because Fibre Channel was
the i rst protocol type used with SANs. However,
SAN
refers to a network topology, not a con-
nection protocol. Although people often use the acronym
SAN
to refer to a Fibre Channel SAN,
you can create a SAN topology using different types of protocols, including iSCSI, FCoE, and
Ini niBand.
SANs were initially deployed to mimic the characteristics of local or direct attached SCSI
devices. A SAN is a network where storage devices (logical units—or LUNs—just as on a SCSI
or SAS controller) are presented from a storage target (one or more ports on an array) to one or
more initiators. An initiator is usually a host bus adapter (HBA) or converged network adapter
(CNA), though software-based initiators are available for iSCSI and FCoE. See Figure 6.7.
Today, Fibre Channel HBAs have roughly the same cost as high-end multiported Ethernet
interfaces or local SAS controllers, and the per-port cost of a Fibre Channel switch is about twice
that of a high-end managed Ethernet switch.
Fibre Channel uses an optical interconnect (though there are copper variants), which is used
since the Fibre Channel protocol assumes a very high-bandwidth, low-latency, and lossless
physical layer. Standard Fibre Channel HBAs today support very-high-throughput, 4 Gbps,
