Tech Tip #33: Improved Scalability of the SlipStream Server

As newer technology becomes industry standard, your SlipStream SP server will be able to handle more and more concurrent users. To further this increase in scalability, we're constantly improving the technology of SlipStream SP as we release new versions.

Since these numbers are changing, it's time we updated the scalability projections using the latest available technology.

Documented Numbers for Older Hardware

These are the numbers currently found in our server documentation, and are good references for planning your server hardware. You should plan your server(s) based on the expected maximum number of concurrent users during peak times.

For load test results, we tested against dual Intel® Xeon® processors (with HyperThreading), and dual Opteron^TM x52 processors. SCSI drives were utilized, tested with and without RAID.

300 Concurrent (Logged-In) Users

• 2 x Intel® Xeon® 2.0GHz/OpteronTM x52 series
• 1.5GB DDR SDRAM
• 2 x 36GB SCSI Hard Drives

500 Concurrent (Logged-In) Users

• 2 x Intel® Xeon® 2.4GHz/OpteronTM x52 series
• 2GB DDR SDRAM
• 3 x 36GB SCSI Hard Drives
• Hardware RAID Controller (RAID 0 array)

1100 Concurrent (Logged-In) Users

• 2 x Intel® Xeon® 3.0 GHz/OpteronTM x52 series
• 4GB DDR SDRAM
• 4 x 73GB SCSI Hard Drives
• Hardware RAID Controller (RAID 0 array)

SlipStream SP Test Environment

For the updated load tests, we worked with the most widely-available standard hardware. These were machines with Xeon® (Core^TM2 based) 3.0 GHz processors. The smallest machine tested matched the largest machine used in our old hardware recommendations. The following attributes were common for the test servers:

• Test servers contained dual, quad, and eight processor cores
• Servers contained 4, 6, and 8GB RAM
• Servers all had 4x74GB 15k RPM SCSI hard drives arranged in a RAID 0 array
• Servers all ran a 64-bit CentOS 5.1 operating system

Our Scalability Test Results

Tests with the latest version (6.0.30) and the newer hardware showed the following results:

• 2 CPU cores, 4GB RAM: 800-900 concurrent users
• 2 CPU cores, 8GB RAM: 1400 concurrent users
• 4 CPU cores, 8GB RAM: 1800-1900 concurrent users
• 8 CPU cores, 8GB RAM: 1800-1900 concurrent users

The biggest influence to the scalability numbers appeared to be the amount of RAM used. The numbers also showed that by increasing the number of processors to 4, the scalability numbers also improved. However, additional CPUs didn't change the numbers in any significant way.

Note: In order for the CentOS operating system to take advantage of more than 4GB of RAM, the 64-bit version needs to be used. The SlipStream SP server can run on a 64-bit system, and doesn't need to be compiled as a 64-bit application in order to take advantage of the higher RAM.

Conclusions

There are several methods to increase scalability and performance with hardware:

1. Add more RAM: If you have less than 4GB of RAM on your SlipStream server, the easiest and best way to increase the scalability of the server is to bring it up to 4GB. More RAM will definitely improve scalability
2. SCSI drives in a RAID 0 array: The more drives, the better the performance of the server's cache. RAID 0 is non-redundant, so is not very fault-tolerant, but is a high performer. If you have to compromise performance with redundancy, be sure to use a RAID 10 or RAID 0+1 array, making sure the equivalent of at least 3 drive spindles is reserved for the cache. That means you should have a chassis capable of handling 6 hard drives, at least.
3. More CPUs: With the Core^TM2 chips, each CPU core is a real physical CPU and not a simulation like HyperThreading technology. Results show that by adding more of these to a system, you can increase your scalability levels. If it's affordable for you to do so, you might consider getting the extra processors.
4. It's still cheaper to get more machines than it is to get bigger machines: While RAM is getting cheaper, and hard drives are getting bigger, it's still cheaper to get a dual processor machine with 8GB RAM than it is to get a 4 processor machine. For the price increase, the scalability numbers only about 400-500 more users per machine. Get two boxes instead of one really big one.

If you have any questions about the preceding article, please contact our Technical Support team.