One of the valuable features included in the Storwize V7000 storage system at no extra cost is Easy Tier. Easy Tier continuously monitors data access patterns and will automatically migrate high activity “hot spots” from Hard Disk Drives to Solid State Drives. Easy Tier is a key feature for helping customers increase the cost effectiveness of SSD drives.
IBM developed a utility called Storage Tier Advisor Tool or STAT, to interpret historical usage data from DS8K, SVC, and Storwize V7000 systems. When Easy Tier is enabled on a storage pool, historical data is recorded, regardless of whether SSD disks are present or not. Simply put, STAT reads the historical data files and outputs information that is helpful in determining if there is value to adding SSD storage to a system. I thought I would take a moment to document how to setup and use the STAT tool.
The first step is to download and install the STAT tool. It can be found at the following URL:
http://www-01.ibm.com/support/docview.wss?uid=ssg1S4000935 Edit this URL is no longer valid. The download can be obtained by searching for Storwize V7000 on the IBM Fix Central website. (http://www-933.ibm.com/support/fixcentral/)
The next step is to enable Easy Tier monitoring on an existing or new storage pool. This is done from the CLI with command:
IBM_2076:ISV7K7:admin>svctask chmdiskgrp -easytier on “storagepoolname”
Easy Tier will capture historical performance data over a 24 hour period. The output file can then be downloaded from the support section of the V7000 as shown below.
Once the output file is downloaded and placed in the STAT directory (Program Files\IBM\STAT), the STAT utility can be ran to generate the reports.
The STAT tool will generate a couple of html pages within the STAT\Data_Files\ directory (System Summary and heat_distribute) which can be used to determine the affect of adding SSD drives to a storage pool. As you can see from my text example, 12% of the data was determined to be hot, and by migrating that data to SSD storage I would realize a 60-80% performance improvement.
In case you are curious this storage pool is housing VMware View linked clone disks. The virtual desktops have been running a simulated office worker workload.