IBM System Storage DS3000, Programming Manual

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The default name of the file that contains the performance modeling data is
readLinkStatus.csv
. You can
use any file name, but you must use the
.csv
extension.
The performance modeling metric data are not available until you stop the performance modeling
operation.
You can see the performance modeling data only after you have stopped the performance modeling
operation. You cannot get intermediate results while the modeling is being run. When you stop the
performance modeling tool, a graphical representation of the results appears, but you can view the results
in tabular format by saving the data to a
.csv file. To compare different results, you can run several
performance modeling operations and save each result to a .csv file for each result.
Then you can use a spreadsheet program outside of the storage management software to compare the
data from the
.csv
file. The performance modeling tool does not support the loading of saved files.
The
.csv
File Information
The
.csv
file shows the following information:
v
Performance Read Cache Capacity (GB) – The amount of Performance Read Cache capacity.
v
Performance Read Cache Hits (%) – Derived from cache hits and total reads.
v Average Overall Response Time – This value is calculated by the software and is not the result of
averaging the response times for SSD Reads (Cache Hits), HDD Reads, and HDD Writes.
v
Average Response Time (milliseconds) – This value is the same as the Average Overall Response Time
in the next paragraph.
v
SSD Reads (Cache Hits) – The total number of host reads of SSD cache-enabled volumes that were
satisfied from the Performance Read Cache.
v
Average Response Time – The average response time of the SSD reads (Cache Hits).
v
Percentage of I/Os – An indication of the percentage of SSD reads (Cache Hits).
v
HDD Reads – The total number of host reads of Performance Read Cache-enabled volumes.
Compare the reads relative to writes. The reads need to be greater than the writes for effective
Performance Read Cache operation. The greater the ratio of reads to writes the better the operation of the
cache.
v
Average Response Time – The average response time of the HDD reads.
v
Percentage of I/Os – An indication of the percentage of HDD reads.
v
HDD Writes – The total number of host writes to Performance Read Cache-enabled volumes. Compare
the reads relative to writes. The reads need to be greater than the writes for effective Performance Read
Cache operation. The greater the ratio of reads to writes the better the operation of the cache.
v
Average Response Time – The average response time of the HDD Writes.
v
Percentage of I/Os – An indication of the percentage of HDD Writes.
Understanding Performance Read Cache performance modeling results
When you run the performance modeling tool with a workload that has the same characteristics as you
run in production, the performance modeling tool collects this type of information:
v
Cache hit percentage – The cache-hit percentage indicates the percentage of all read commands that
find data in the Performance Read Cache for each of the cache capacities. For almost all workloads, a
cache-hit percentage around 75 percent indicates that you have sufficient capacity. A cache-hit
percentage much higher than this means that the workload performance is likely to be improved with
more Performance Read Cache capacity. However, for some workloads, a cache-hit percentage around
50 percent or even lower indicates that you have sufficient capacity.
10-4
IBM System Storage DS3000, DS4000, and DS5000: Command Line Interface and Script Commands Programming Guide