User guide

139MAXDATA SR1202 M1 – StorView
®
RAID User Guide
Statistic Description
Read-Ahead Command Hit Rate
This is the percentage of read command hits
versus the total number of read commands that
have been issued. This gives an indication of the
sequential nature of the data access pattern from
the host.
Read-Ahead Command Efficiency
This is the percentage of the number of read
command hits versus the projected number of
read-ahead command hits. This is a measure
of the efficiency of the read-ahead algorithm. A
low value means that much of the data that the
controller reads in the read-ahead command is
not actually requested by the host.
Command Cluster Statistics
To increase performance, the controller can cluster sequential write commands together to create
a larger write command. This results in less commands being sent to the disk drives. Additionally,
if sufficient data is clustered by the controller, then it can perform a a full stripe write for RAID5/50
arrays. This significantly improves performance. In cases where the host does not send a sufficient
number of outstanding writes, writeback cache can be used to delay the write to disk, increasing the
likelihood of clustering more data.
Figure 109. Statistics Screen - Command Cluster Tab