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Optimizing RAID Performance: Benchmarks

Optimizing RAID Performance: Benchmarks
September 24
17:10 2008

A RAID configuration is a series of hard disks acting together as one drive in your system. Some configurations, such as RAID-1, ensure not only that if one drive fails the other drive(s) in your array still have a complete record of your data, but also that your server is still able to operate with the disabled drive. The wrong RAID configuration, however, can seriously impact the performance of your machine. There are two important aspects to consider when choosing the right solution for your servers. First, will the drive primarily be doing sequential reads, sequential writes, or random I/O functions; and second, should you enable write cache? INetU recently performed a benchmark test to highlight the differences in RAID-1, RAID-5, and RAID-10 in terms of performance in regards to these aspects.

About RAID
A RAID configuration is used to join a series of hard disks together to make redundant copies of data, to improve hard drive performance, or both. The simplest configuration in this benchmark is RAID-1, which requires two hard disks. Each disk in the array is an exact copy of the other, so that only one drive is required for data integrity. In a RAID-5 configuration, three or more disks are joined together in an array. The data, along with additional information (parity) is distributed across the array allowing any one disk to be removed without a loss of data. Lastly, a RAID-10 configuration is a nested RAID level where data is split between two sets of drives in a RAID-1 configuration in order to boost the overall drive performance.

Sequential Reads
A server that is primarily responsible for sequential reads is one that rarely writes data to the hard drive but often reads files in prescribed patterns, such as a web server. As illustrated in Figure 1, our benchmark results show that RAID-5 seriously hinders sequential read performance. Both RAID-1 and RAID-10 are able to perform sequential reads well. Keeping the write cache disabled provides a minor additional increase to this performance because the cache can be devoted to reads.

Sequential Writes
Database applications are primarily the main application that uses a sequential write, such as writing transaction logs. Our benchmark results (Figure 2) show that RAID-5 provides the fastest sequential write performance, followed by RAID-10 and then RAID-1. In every instance, there is a dramatic performance increase by enabling write cache. Because the writes are following a systematic pattern, the RAID configurations performing sequential writes benefit greatly from the ability to perform RAID-level caching.

Random I/O
Most applications, especially operating systems, perform both reads and writes in a random manner. Figure 3 shows the results of our benchmark test. RAID-10 performed at double the speed of RAID-1 and performed about 33% better than RAID-5. Thus RAID-10 provides the best performance for the I/O demands of most applications. Enabling write cache provided an increase in performance proportional to the amount of RAM installed on the RAID controller.

Want to optimize your performance?
If you are interested in learning more about RAID performance, contact INetU Managed Hosting.  Their Solutions Consultant can help you find the solution that is right for your needs.

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