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From koji Lin <koji....@gmail.com>
Subject Re: Using EC2 ephemeral 4disk raid0 cause high iowait trouble
Date Fri, 18 May 2012 01:59:39 GMT
Hi

We use amazon ami 3.2.12-3.2.4.amzn1.x86_64

and some of our data file are more than 10G

thanks

koji
2012-5-16 下午6:00 於 "aaron morton" <aaron@thelastpickle.com> 寫道:

> On Ubuntu ? Sounds like http://wiki.apache.org/cassandra/FAQ#ubuntu_hangs
>
> Cheers
>
>
> -----------------
> Aaron Morton
> Freelance Developer
> @aaronmorton
> http://www.thelastpickle.com
>
> On 16/05/2012, at 2:13 PM, koji Lin wrote:
>
> Hi
>
> Our service already run cassandra 1.0 on 1x ec2 instances(with ebs), and
> we saw lots of discussion talk about using  ephemeral raid for better
> performance and consistent performance.
>
> So we want to create new instance using 4 ephemeral raid0, and copy the
> data from ebs to finally replace the old instance and reduce some .
>
> we create the xlarge instance with -b '/dev/sdb=ephemeral0' -b
> '/dev/sdc=ephemeral1' -b '/dev/sdd=ephemeral2' -b '/dev/sde=ephemeral3',
>
> and use mdadm command like this  mdadm --create /dev/md0 --level=0 -c256
> --raid-devices=4 /dev/sdb /dev/sdc /dev/sdd /dev/sde
>
> after copying file and start the cassandra(same token as old instance it
> replaced).
>
> we saw the read is really fast always keep 2xxm/sec, but system load
> exceed 40, with high iowait, and lots of client get timeout result. We
> guess maybe it's the problem of ec2 instance, so we create another one with
> same setting to replace other machine ,but the result is same . Then we
> rollback to ebs with single disk ,read speed keeps at 1xmb/sec but system
> becomes well .(using ebs with 2 disks raid0 will keep at 2xmb/sec and
> higher iowait then single disk ,but still works)
>
> Is there anyone meet the same problem too ? or do we forget something to
> configure?
>
> thank you
>
> koji
>
>
>

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