Dell Power Solutions

STORAGETwo performance metrics help delineate the capabilities ofNAS servers:12001000• Maximum performance testing: Determines the maximumperformance boundary of the NAS server under stress. Maximumperformance testing strives to achieve the best possible(peak) performance without manipulating the I/O.• Scalability testing: Examines NAS performance behavior atdifferent concurrent user loads. Scalability testing varies userloads, I/O ratios, user wait states, and file sizes to simulatethe most common types of real-world user activity.Throughput (Mbps)800600400200RAID-5RAID-000 10 20 30 40 50 60Number of clientsResults from maximum performance testing are used mainly tocompare the performance of different NAS servers. The results canalso identify the point at which NAS server resources become overutilized.However, by examining only maximum performance results,storage administrators may have difficulty determining performancebehavior in various real-world environments. Instead, administratorscan use scalability results to accurately determine which andhow many NAS units fit best in a given computing scenario.Scalability testing can also identify networking configuration anddeployment pitfalls to avoid.Testing the PowerVault 770N for maximum performanceDell measured the peak performance of a PowerVault 770N NASserver configured as follows:• Memory: 4 GB of 266 MHz double data rate (DDR) SDRAM• Storage: Four 15,000 rpm, 18 GB Ultra320 (U320) SCSI harddisk drives• Network connectivity: Intel ® PRO/1000+ LAN on Motherboard(LOM)• RAID controller: Dell PowerEdge Expandable RAID Controller4, Dual Channel integrated (PERC 4/Di) with 128 MBbattery-backed cache (default settings); tested RAID levelswere RAID-0 and RAID-5• Processor: Dual Intel Xeon processors, including the IntelXeon processor at 2.8 GHz with 512 KB of level 2 (L2) cache,the Intel Xeon processor at 3.06 GHz with 512 KB of L2cache, the Intel Xeon processor at 3.06 GHz with 512 KB ofL2 and 1 MB of level 3 (L3) cache, and the Intel Xeon processorat 3.2 GHz with 512 KB of L2 and 1 MB of L3 cacheAll performance tests used 60 Dell OptiPlex GX1 desktopcomputers as network clients to generate network throughput andcreate the necessary client load. Each client contained a 1 GHzprocessor and an Intel PRO/100+ network interface card (NIC).Figure 1. Effect of RAID type on throughput for the maximally configured PowerVault 770NBecause the clients ran the Microsoft Windows XP Professionaloperating system, CIFS was used as the file-sharing protocol. Theclients and the PowerVault 770N were connected through a DellPowerConnect 3024 switch.To produce performance results for the PowerVault 770N, Dellused version 7.0.3 of the Ziff Davis ® NetBench ® portable benchmarktool. 1 NetBench generates client workloads using file types similarto those supported by common Windows-based applications.NetBench produces results for throughput and average I/Oresponse time. Throughput, reported in megabits per second (Mbps),is the rate at which data is transferred between the server and itsnetwork clients. Average response time, reported in milliseconds(ms), is the average amount of time the server takes to respond toand complete network client requests at a given client load. Averageresponse times are inversely proportional to throughput: thehigher the response time, the lower the throughput. Greater throughputmeans faster performance. These results help reveal when thePowerVault 770N reaches a critical threshold, which is the point atwhich response times begin to increase and the NAS server runs ina suboptimal state.Note that no correlation exists between the number of NetBenchtest clients and the scalability potential of the PowerVault 770N. Toquickly obtain the peak throughput for a server during a test run,NetBench clients are asked to produce an unrealistic volume ofcommon network file operations.Effect of RAID configuration and processor cacheAs shown in Figure 1, the peak throughput for RAID-0 on the maximallyconfigured PowerVault 770N (containing 4 GB of DDR SDRAMand dual Intel Xeon processors at 3.2 GHz with 1 MB of L3 cacheand Hyper-Threading enabled) is 1011 Mbps (126 MB/sec). TheRAID-5 storage configuration achieves a peak throughput of 817 Mbps1 For more information about NetBench, see http://www.etestinglabs.com/benchmarks/netbench/default.asp.www.dell.com/powersolutions POWER SOLUTIONS 107