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this 2 days, i faced very weird problem. When i'm doing uncompress big file, the iowait become very high, more than 70% I do iotop and the result got 3 process with high IO

gzip -d filename 
[flush-202:1]
[jbd2/xvda1-8]

when the process run, the available memory(RAM) also still around 4gb. Because of this, all the process become bottleneck, make the server become slow. But after the extract file finish, these 2 process still there [flush-202:1] & jbd2/xvda1-8] with high IO .

I've tried to create AMI from this EC2 and launch new instance using this AMI, but the result still same . The iowait still high .

any body face same problem before ?

Thanks for your help.

note: server run using Amazon Linux , 3.4.48-45.46.amzn1.x86_64 .

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Is this on an ELB volume or an ephemeral volume? –  David Schwartz Oct 22 '13 at 18:06

1 Answer 1

up vote 1 down vote accepted

This sounds perfectly normal. If you ask the server to do lots of I/O, then I/O becomes slow because processes have to wait their turn. If you're willing to slow down the uncompression to keep responsiveness high, you can do so using ionice or ratepipe.

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