DELL MD3220 사용자 설명서

Planning: MD3200 Series Storage Array Terms and Concepts

A load balance policy is used to determine which path is used to process I/O. 

Multiple options for setting the load balance policies lets 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 

might 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.

book.book  Page 54  Monday, June 21, 2010  11:00 AM