Many have asked me "will FlashCache help me in my environment". Well, the answer depends on the degree to which your workload exhibits small, random reads. This, of course, begs another question: "What's does my workload exhibit?".
So, now, to avoid a Catch 22 ;-) , my task is to define and explain steps so that I can help you know:
#1 Enabling FlashCache simulation aka PCS
TR-3801 will tell you how to use PAM II simulation. Please read : http://www.netapp.com/us/library/technical-reports/tr-3801.html
“NetApp® Predictive Cache Statistics (PCS) offer the ability to emulate large read cache sizes and to
measure their effect on system performance. In this way PCS provides a means to approximate the
performance gains of adding one or more Performance Acceleration Modules (PAM or PAM II) to a system.”
Since quick approach might be preferred with less reading, follow these steps:
#2 Running perfstat
-- perfstat -f ___<hostname-of-a-controller>__ -t 30 -i 46 > perfstat-<hostname-of-a-controller>"Date_%date:~4,2%%date:~7,2%%date:~10,4%-Time_%time:~0,2%h%time:~3,2%m%time:~6,2%s"
-- Don't forget to run for each controller
-- Example will capture 46 samples of 30 minute intervals. This is a total of 23 hours.
-- Since perfstat uses rsh commands and the time to complete the rsh's can vary, it often runs for slightly longer than the specified time. To compensate for this (and not have 2 perfstat tools running concurrently), we recommend a 23 hour run to cover a 24 hour period.
#3 Sending via FTP
#4 Wrapping Up
Please don’t hesitate to ask any questions. Thank you!
NetApp Enterprise SE
Regarding running the FlashCache simulation aka PCS. I haven't personally run this and I probably won;t get the chance, however I do have multiple channel partners who ask many questions around this. I have read through the TR-3801, I was wondering you you had or knew where I could potentially find an FAQ around PCS.
The question I have is "What is the typical/expected/estimated system overhead when running the PCS?".
The reason I ask this, is I have a partner who has a customer running a system at nearly maximum utilisation and they was wondering whether its safe to run this PCS tool on this system or will it require 5-10% system overhead?
Does it depend on the ONTAP versions there running? 7.3.x vs 8.0.x vs 8.1.x vs 8.2.x
Are there any other caveats/gottcha they should look out for if and when running this tool?
Many thanks in advance.
NetApp recommends issuing this command through an SSH connection and logging the output throughout the observation period because you want to capture and observe the peak performance of the system and the cache. This output can also be easily imported into spreadsheet software, graphed, and so on. A second SSH can be used to capture the output of the sysstat command. The combination of these two data points, PCS-specific and system data, lets you know what is happening on the system and how the emulated cache that PCS is presenting would handle the workload. PCS will run on any system capable of having FlashCache installed and will not impact the current system performance while running. PCS can be run on systems starting with ONTAP 7.3.2 and up to all current versions including Clustered ONTAP.
NetApp Commercial SE