Dell PowerVault MD3820f - Manual (Page 34)

Load Balancing
A load balance policy is used to determine which path is used to process I/O. Multiple options for setting
the load balance policies let you optimize I/O performance when mixed host interfaces are configured.
You can choose one of these load balance policies to optimize I/O performance:
• Round-robin with subset — The round-robin with subset I/O load balance policy routes I/O requests,
in rotation, to each available data path to the RAID controller module that owns the virtual disks. This
policy treats all paths to the RAID controller module that owns the virtual disk equally for I/O activity.
Paths to the secondary RAID controller module are ignored until ownership changes. The basic
assumption for the round-robin policy is that the data paths are equal. With mixed host support, the
data paths may have different bandwidths or different data transfer speeds.
• Least queue depth with subset — The least queue depth with subset policy is also known as the least
I/Os or least requests policy. This policy routes the next I/O request to a data path that has the least
outstanding I/O requests queued. For this policy, an I/O request is simply a command in the queue.
The type of command or the number of blocks that are associated with the command are not
considered. The least queue depth with subset policy treats large block requests and small block
requests equally. The data path selected is one of the paths in the path group of the RAID controller
module that owns the virtual disk.
• Least path weight with subset (Windows operating systems only) — The least queue depth with subset
policy is also known as the least I/Os or least requests policy. This policy routes the next I/O request
to a data path that has the least outstanding I/O requests queued. For this policy, an I/O request is
simply a command in the queue. The type of command or the number of blocks that are associated
with the command are not considered. The least queue depth with subset policy treats large block
requests and small block requests equally. The data path selected is one of the paths in the path
group of the RAID controller module that owns the virtual disk.
Monitoring System Performance
Performance Monitor allows you to track a storage array’s key performance data and identify
performance bottlenecks in your system. You can use Performance Monitor to perform these tasks:
• View in real time the values of the data collected for a monitored device. This capability helps you to
determine if the device is experiencing any problems.
• See a historical view of a monitored device to identify when a problem started or what caused a
problem.
• Specify the performance metric and the objects that you want to monitor.
• View data in tabular format (actual values of the collected metrics) or graphical format (as line graphs),
or export the data to a file.
Three types of performance monitoring exist:
• Real-time graphical – Plots performance data on a graph in near real-time.
• Real-time textual – Shows performance data in a table in near real-time.
• Background (historical) – Plots graphical performance data over a longer period of time. You can
view background performance data for a session that is currently in progress or for a session that you
previously saved.
This table shows some specific characteristics of each type of performance monitoring:
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