742 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
Performance monitoring
This section highlights several performance monitoring techniques.
Collecting performance statistics
IBM Spectrum Virtualize is constantly collecting performance statistics. The default frequency 
by which files are created is 5-minute intervals. The collection interval can be changed by 
using the startstats command. 
The statistics files for volumes, managed disk (MDisks), nodes, and drives are saved at the 
end of the sampling interval. A maximum of 16 files (each) are stored before they are overlaid 
in a rotating log fashion. This design then provides statistics for the most recent 240-minute 
period if the default 15-minute sampling interval is used. IBM Spectrum Virtualize supports 
user-defined sampling intervals of 1 - 60 minutes.
For each type of object (volumes, MDisks, nodes, and drives), a separate file with statistic 
data is created at the end of each sampling period and stored in /dumps/iostats.
Use the startstats command to start the collection of statistics, as shown in Example A-1.
Example A-1   The startstats command
IBM_Storwize:ITSO-V7k:superuser>startstats -interval 2
This command starts statistics collection and gathers data at 2-minute intervals.
To verify that the statistics collection interval, display the system properties again, as shown in 
Example A-2.
Example A-2   Statistics collection status and frequency
IBM_Storwize:ITSO-V7k:superuser>lssystem
statistics_status on 
statistics_frequency 2
-- The output has been shortened for easier reading. --
It is not possible to stop statistics collection with the command stopstats starting with V8.1.
Statistics are collected per node. The sampling of the internal performance counters is 
coordinated across the cluster so that when a sample is taken, all nodes sample their internal 
counters at the same time. It is important to collect all files from all nodes for a complete 
analysis. Tools, such as IBM Spectrum Control, perform this intensive data collection for you.
Statistics file naming 
The statistics files that are generated are written to the /dumps/iostats/ directory. The file 
name is in the following formats:
/SM590000Nm_stats_<node_id>_<date>_<time> for MDisks statistics
Collection intervals: Although more frequent collection intervals provide a more detailed 
view of what happens within IBM Spectrum Virtualize and Storwize V7000, they shorten 
the amount of time that the historical data is available on the IBM Spectrum Virtualize. For 
example, rather than a 240-minute period of data with the default 15-minute interval, if you 
adjust to 2-minute intervals, you have a 32-minute period instead.