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NAS Too Slow? Try iSCSI

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Introduction

In most of our reviews, we tend to focus on the performance of reading and writing large files. Our Windows Filecopy benchmark uses a ripped DVD folder with a few 1 GB VOB files and a mix of smaller files. And the NASPT File Copy tests read and write a single 1.15 GB windows backup file. NAS shoppers (and manufacturers) like to focus on these benchmarks because they produce the highest numbers.

Intel NASPT File Copy to NAS  Benchmark - 4 drive NASes, RAID 0

Intel NASPT File Copy to NAS Benchmark - 4 drive NASes, RAID 0

As an example, look at the NASPT File Copy To and From NAS charts shown above and below. These are for RAID 0 volumes and filtered for four-bay NASes. The NASes ranking at the top are based on dual-core Intel Atom CPUs, while those toward the bottom run on less-expensive (and powerful) Marvell SoCs.

Intel NASPT File Copy to NAS  Benchmark - 4 drive NASes, RAID 0

Intel NASPT File Copy to NAS Benchmark - 4 drive NASes, RAID 0

I was talking to someone the other day about high-end NASes and remarked that even multi-core processors can't do much to improve the performance of small file reads and writes on NASes. This is illustrated best by the NASPT Content Creation and Office Productivity benchmarks.

According to Intel's description, the Content Creation benchmark is a "scripted routine simulating a user creating a web advertisement from various content sources including video and 3D modeling software. 95% writes with mix of 1k, 4k & little reads. Wide range of writes up to 64kB, mostly sequential". Although there is almost a 2X difference between lowest and highest performance products in the chart below, 14 MB/s is still nothing to write home about.

Intel NASPT Content Creation Benchmark - 4 drive NASes, RAID 0

Intel NASPT Content Creation Benchmark - 4 drive NASes, RAID 0

The Office Productivity benchmark has more of a balance of reads and writes, i.e. "Common productivity applications: e-mail, spreadsheet, etc. running scripted routines. Balance of reads & writes, mostly 1k & 4k reads with a large number of smaller reads. Mostly 1kB writes, mostly sequential accesses". The chart of this benchmark, for the same group of NASes produces higher throughput, but less of a spread between lowest and highest performance.

Intel NASPT Content Creation Benchmark - 4 drive NASes, RAID 0

Intel NASPT Content Creation Benchmark - 4 drive NASes, RAID 0

Given the huge difference in performance, it's hard to believe these charts are showing the same group of NASes! But no amount of processing power can overcome the overhead involved with moving data over a network. Certain bits have to go into each packet to ensure that all the data you send safely arrives at the other end.

When the chunk of data you are moving is big, those overhead bits are a relatively small percentage of the network bandwidth used. But as file sizes get smaller, the overhead packets stay the same size and use up a much larger percentage of transmission time.




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