HP XP Array Manager Software - Manual (Page 20)

that DRR usage is not balanced, you should consider relocating volumes using Auto LUN to balance
DRR usage within the storage system.
For details on how to view usage statistics on DRRs, see
“ Viewing Usage Statistics about Data Recovery and Reconstruction Processors (DRRs) ” on page 57.
Write Pending Rate and Cache Memory Usage Statistics
The write pending rate indicates the ratio of write-pending data to the cache memory capacity. The
Auto LUN window displays the average and the maximum write pending rate for the specified period
of time. When you display monitoring results in a short range, the window also displays the average
and the maximum usage statistics about the cache memory for the specified period of time. In addition,
the window can display a graph that indicates how the write pending rate or the usage statistics of
the cache memory changed within that period.
For details on how to view the write pending rate and the usage statistics about the cache memory, see
“ Viewing Write Pending and Cache Memory Usage Statistics ” on page 58.
Access Path Usage Statistics
An access path is a path through which data and commands are transferred within a storage system.
In a storage system, channel adapters control data transfer between hosts and the cache memory. Disk
adapters control data transfer between the cache memory and hard disk drives. Data transfer does not
occur between channel adapters and disk adapters. Data is transferred via the cache switch (CSW)
to the cache memory.
When hosts issue commands, the commands are transferred via channel adapters to the shared memory
(SM). The content of the shared memory is checked by disk adapters.
D KA D KA D KA D KA
C H A C H A C H A C H A
cache sw itch （C SW ）
cache
m em ory
CHA: channel adapter
DKA: disk adapter
shared
m em ory
Figure 2 Access Paths
Performance Monitor tracks and displays the usage rate for the following access paths.
• Paths between channel adapters and the cache switch
• Paths between disk adapters and the cache switch
• Paths between the cache switch and the cache memory
• Paths between channel adapters and the shared memory
• Paths between disk adapters and the shared memory
For details on how to view usage statistics about access paths, see
“ Viewing Usage Statistics about Access Paths ” on page 60.
Hard Disk Drive Workload Statistics
If particular hard disk drives or data are heavily accessed, system performance might deteriorate.
Performance Monitor lets you view statistics about parity groups and logical devices to help you detect
bottlenecks in your system. If you mapped volumes in an external storage system, Performance Monitor
20 About Performance Monitor