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From Chris Dodge <chrisndo...@hotmail.com>
Subject Re: Cassandra, AWS and EBS Optimized Instances/Provisioned IOPs
Date Fri, 14 Sep 2012 15:29:51 GMT

Michael Theroux <mtheroux2 <at> yahoo.com> writes:

> 
> Hello,
> A number of weeks ago, Amazon announced the availability of EBS Optimized
instances and Provisioned IOPs for Amazon EC2.  Historically, I've read EBS is
not recommended for Cassandra due to the network contention that can quickly
result (http://www.datastax.com/docs/1.0/cluster_architecture/cluster_planning).
> 
> Costs put aside, and assuming everything promoted by Amazon is accurate, with
the existence of provisioned IOPs, is EBS now a better option than before?
 Taking the points against EBS mentioned in the link above:
> 
> 
> EBS volumes contend directly for network throughput with standard packets.
This means that EBS throughput is likely to fail if you saturate a network link.
> According to Amazon, Provisioned IOPS guarantees to be within 10% of  of the
provisioned performance 99.9%of the time.  This would mean that throughput
should no longer fail.
> EBS volumes have unreliable performance. I/O performance can be exceptionally
slow, causing the system to backload reads and writes until the entire cluster
becomes unresponsive.
> Same point as above.
> Adding capacity by increasing the number of EBS volumes per host does not
scale. You can easily surpass the ability of the system to keep effective buffer
caches and concurrently serve requests for all of the data it is responsible for
managing.
> I believe this may be still true, although I'm not entirely sure why this is
more true for EBS volumes vs. emphemeral.
> 
> Any real world experience out there with these new EBS options?
> 
> -Mike
> 
> 
> 

Thanks for asking this as I'm wondering the same thing. I'd like to hear other
people's take on this as I'm trying to spec out a Cassandra ring on AWS.





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