On Wed, Jan 27, 2010 at 10:16:12PM -0500, Yuehai Xu wrote:

md0 : active raid5 sdh1[7] sdg1[5] sdf1[4] sde1[3] sdd1[2] sdc1[1] sdb1[0]
      631353600 blocks level 5, 64k chunk, algorithm 2 [7/6] [UUUUUU_]

[...]

Then I start IOZONE which starts 10 processes to do the sequential
read(iozone -i 1). Each process read 640M file on each partition. The
throughput of RAID0 is about 180M/s, while the throughput of RAID5 is
just 43M/s. Why the performance between RAID0 and RAID5 is so
different?

You have a degraded RAID5 array with one drive missing, meaning the data
has to be recalculated from parity all the time. That obviously kills
performance.

Gabor

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     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
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