High Performance
One of the key features of SAN storage systems is their high performance and low response time compared to other storage structures such as DAS. Ever increasing need for fast and reliable data access mandates efficient, high-performance SAN storage systems.
The most important metrics for measuring the performance of data storage systems are as follows:
Bandwidth (BW) is generally referred to the amount of data read/write storage system
can handle in one second (in MB/s or GB/s units), demonstrating the capability of
storage system in handling sequential requests. The storage bandwidth is a function
of the bandwidth of disk array, internal interconnections (such as interconnections
between controllers and disk subsystem), and external connections (such as
connection between storage system and hosts). The highest bandwidth usage is
observed when the requests are sequential with big size (as an example we can note
multimedia applications). Storage manufacturers report the storage bandwidth for the
sequential big requests that can use the maximum storage bandwidth. In practice,
however, the bandwidth may be lower than the reported bandwidth depending on the
workload characteristics.
HDDs have low read/write performance due to their physical characteristics. This is not a big issue in home applications where the HDD is responsible to just one user. However, in the data storage systems that are responsible to handle multiple hundred thousands of requests per second, the low performance of HDDs becomes a major bottleneck. The enterprise HDDs can deliver 200 MBPS in the ideal situations, while a data storage system needs to provide over 100 GBPS throughput. SAN storage systems provide this high bandwidth using a combination of disk redundancies (such as RAID mechanisms), caching mechanisms, and data tiering mechanisms that mandate using many extra hardware/software modules such as DRAMs, SSDs, and controllers.
IOPS is a function of various parameters such as workload characteristics and data access time (from disk subsystem). For example, a DSS can deliver higher IOPS when the size of requests is relatively small. We need to note that a DSS may deliver a great IOPS with a poor Response Time, when the data access time is high. Hence, IOPS is not enough for reporting the performance of DSS, while Response Time has also important impact on DSS performance. IOPS is typically reported for workloads with small request size (4 and 8 KB) with random access pattern. Following table reports the results of few tests on a single HDD:
| IOPS | زمان پاسخ (ms) | درصد درخواستهای خواندن | درصد درخواستهای متوالی | اندازه درخواست (KB) | ردیف |
|---|---|---|---|---|---|
| 29736 | 0 | 100 | 100 | 4 | 1 |
| 236 | 4.2 | 100 | 60 | 4 | 2 |
| 140 | 7.1 | 100 | 30 | 4 | 3 |
| 100 | 10 | 100 | 0 | 4 | 4 |
| 293 | 3.4 | 60 | 100 | 4 | 5 |
| 168 | 5.9 | 30 | 100 | 4 | 6 |
| 7658 | 0.1 | 100 | 100 | 16 | 7 |
| 210 | 4.7 | 100 | 60 | 16 | 8 |
| 130 | 7.7 | 100 | 30 | 16 | 9 |
| 98 | 10.1 | 100 | 0 | 16 | 10 |