vSphere Storage - ESXi 5.1 - Documentation - VMware

Because each application has different requirements, you can meet these goals by choosing an appropriate
RAID group on the storage system. To achieve performance goals, perform the following tasks:
n Place each LUN on a RAID group that provides the necessary performance levels. Pay attention to the
activities and resource utilization of other LUNS in the assigned RAID group. A high-performance RAID
group that has too many applications doing I/O to it might not meet performance goals required by an
application running on the ESXi host.
n Provide each server with a sufficient number of network adapters or iSCSI hardware adapters to allow
maximum throughput for all the applications hosted on the server for the peak period. I/O spread across
multiple ports provides higher throughput and less latency for each application.
n To provide redundancy for software iSCSI, make sure the initiator is connected to all network adapters
used for iSCSI connectivity.
n When allocating LUNs or RAID groups for ESXi systems, multiple operating systems use and share that
resource. As a result, the performance required from each LUN in the storage subsystem can be much
higher if you are working with ESXi systems than if you are using physical machines. For example, if you
expect to run four I/O intensive applications, allocate four times the performance capacity for the ESXi
LUNs.
n When using multiple ESXi systems in conjunction with vCenter Server, the performance needed from the
storage subsystem increases correspondingly.
n The number of outstanding I/Os needed by applications running on an ESXi system should match the
number of I/Os the SAN can handle.
Network Performance
A typical SAN consists of a collection of computers connected to a collection of storage systems through a
network of switches. Several computers often access the same storage.
Single Ethernet Link Connection to Storage shows several computer systems connected to a storage system
through an Ethernet switch. In this configuration, each system is connected through a single Ethernet link to
the switch, which is also connected to the storage system through a single Ethernet link. In most configurations,
with modern switches and typical traffic, this is not a problem.
Figure 14-1. Single Ethernet Link Connection to Storage
Chapter 14 Best Practices for iSCSI Storage
When systems read data from storage, the maximum response from the storage is to send enough data to fill
the link between the storage systems and the Ethernet switch. It is unlikely that any single system or virtual
machine gets full use of the network speed, but this situation can be expected when many systems share one
storage device.
When writing data to storage, multiple systems or virtual machines might attempt to fill their links. As Dropped
Packets shows, when this happens, the switch between the systems and the storage system has to drop data.
This happens because, while it has a single connection to the storage device, it has more traffic to send to the
storage system than a single link can carry. In this case, the switch drops network packets because the amount
of data it can transmit is limited by the speed of the link between it and the storage system.
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