User guide

140 Statistics
Statistic Description
Write Cluster Rate
This is the percentage of the number of write
commands that are part of a cluster versus the
total number of write commands that have been
issued. This gives an indication of the sequential
nature of the data access pattern from the host,
and of the performance of the writeback cache.
RAID 5/50 Full Stripe Write Rate
This is the percentage of the amount of data that
is written as a full stripe write versus the total
amount of data written. This gives an indica
-
tion of the sequential nature of the data access
pattern from the host, and of the performance of
the writeback cache, for RAID 5/50 drive ranks.
Command Cluster Count When the controller clusters a write command,
it may cluster a large number of them together.
These statistics record the average and maximum
number of commands the controller clusters, and
also the percentage for each one of these values.
Command Cluster Interval In determining whether to cluster write
commands or not, the controller will search back
in the command queue whenever it receives a
new write command. In a multi threaded oper-
ating system, commands from each thread may
be interspersed with commands from another
thread. This requires that the controller not just
check the immediately previous command.
The controller will search back for a number
of commands, to try to determine if the new
command is exactly sequential to any one of
these previous commands. If it is, then the
controller determines that it can cluster these
commands.
These statistics record the average and maximum
number of commands the controller must search
back for when it finds a sequential command
match, and also the percentage for each one of
these values.