SPEC SFS 2008: The Benefit of the Performance Acceleration Module

Back in August I posted an entry regarding NetApp's Performance Acceleration Module (PAM). To summarize, the PAM card is a 16GB DRAM based read cache integrated with ONTAP that shipped around the middle of 2008. Depending on the platform, up to 5 modules can be installed for a maximum of 80GB of intelligent read cache.

The caching policies implemented as part of ONTAP in conjunction with the usage of the PAM(s) are designed to discern random from sequential reads and hold on to these blocks in cache in order to minimize back-end disk reads which can add latency.

In that article, I also said that an additional PAM benefit is that it can, potentially, provide significant reduction in terms of  the number of disks and shelves to be deployed in order to support the same application(s), thus reducing costs, while providing great response times.

Today, we announced results using the new SPEC SFS 2008 Benchmark  to test 3 configurations. For more on the Specifics of the SPEC SFS 2008 Benchmark, Mike Eisler has a couple of great posts here and here.

The individual benchmarks results can be be found below:

• FAS3140 + 224 15k RPM FC Disks
• FAS3140 + 112 15k RPM FC Disks + 2 PAM Modules (16GB each)
• FAS3140 + 112 7.2k RPM SATA Disks + 2 PAM Modules (16GB each)

However, thru the good work of a co-league of mine, the results from the 3 configurations have been summarized on the below chart:

 

Based on the specific results the conclusion one can easily arrive to is that:

• SATA is a viable option ,given that it is possible to increase storage capacity by 75%, reduce disks by 50% and still achieve highly acceptable levels of performance. 
• Improve response times, by 35% using FC drives while reducing the number of drives by 50%

Starting with DataONTAP 7.2.6.1, we've provided the ability thru the collection of Predictive Cache Statistics (PCS) to determine whether specific workloads will benefit from the deployment of PAM modules and with what significance.

 

Technorati Tags: Performance Acceleration Module,PAM,NetApp SPEC SFS 2008

Comments

[Fletch]

Our (ONTAP 7.3) FAS3040 cluster is dropping frames due to no buffer as reported by ifstat -a.
The heads are not otherwise CPU or IOP bound.
Your response time analysis is useful, but would we benefit from PAM cards in our case of interface buffer exhaustion?

thanks

[Nick Triantos]

Fletch,

Since you're running 7.3 unpatched, I recommend opening a support case on this. As far as the PAM goes, NetApp has introduced a tool called Predictive Cache Statistics. It's available on systems running ONTAP 7.3 and above. It collects data and reports what the cache hit ratio would be if the system had 2x, 4x or 8x the current cache size.

Here's an excellent blog about it

http://ctistrategy.com/2009/02/27/netapp-cache-pcs/

[Jesse St. Laurent]

Nick, Thanks for the compliment.

Fletch, If you have any questions, feel to post a comment on the post Nick linked to and I will get you an answer.

- Jesse