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Re: A little RAID experiment

To: xfs@xxxxxxxxxxx
Subject: Re: A little RAID experiment
From: Joe Landman <landman@xxxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 27 Apr 2012 11:28:53 -0400
In-reply-to: <CAAxjCExzLXGMw2O32kR8xGS6-EpfwfKm-zkM0Vy58bryWygZuQ@xxxxxxxxxxxxxx>
Organization: Scalable Informatics
References: <CAAxjCEzh3+doupD=LmgqSbCeYWzn9Ru-vE4T8tOJmoud+28FDQ@xxxxxxxxxxxxxx> <1335363423.4586.431.camel@xxxxxxxxxxxxxxxxxxxxxxxx> <CAAxjCExzLXGMw2O32kR8xGS6-EpfwfKm-zkM0Vy58bryWygZuQ@xxxxxxxxxxxxxx>
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On 04/26/2012 04:53 AM, Stefan Ring wrote:

I just want to stress that our machine with the SmartArray controller
is not a cheap old dusty leftover, but a recently-bought (December
2011) not exactly cheap Blade server, and that’s all you get from HP.

We have an anecdote about something akin to this which happened 2 years ago. A potential customer was testing a <insert large multi-letter acronym brand name here> machine to run a specific set of software which tightly coupled to its disks. Performance was terrible. Our partner (the software vendor) contacted us and asked us to help. We'd suggested that the partner loan them the machine they had bought from us 2 years earlier (at the time) and try that.

Our 2 year old machine (actually 2 generations back at the time of test, now 5 generations behind our current kit) wound up being more than an order of magnitude faster than the (then) latest and greatest kit from <insert large multi-letter acronym brand name here>.

The lesson is this. Latest and greatest doesn't mean fastest. Design, and implementation matter. Brand names don't.

To this day, we still see machines being pushed out with PCIx technology for networking, or disk, or ...

... and customers buy it up, for reasons that have little to do with performance, suitability to the task, etc.

If you need performance, its important to focus some effort upon locating systems/vendors capable of performing where you need them to perform. Otherwise you may wind up with a warmed over web server with some random card and a few "fast" disks tossed in.

I don't mean to be blunt, but this is basically what you were sold. Note also, I see this in cluster file system bits all the time. We get calls from people, who describe a design, and ask us for help making them go fast. We discover that they've made some deep fundamental design decisions very poorly (usually upon the basis of what <insert large multi-letter acronym brand name here> told them were options), and there was no way to get between point A (their per unit performance) and point B (what they were hoping for as an aggregate system performance).

At the most basic level, your performance will be modulated by your slowest performing part. You can put infinitely fast disks on a slow controller, and your performance will be terrible. You can put slow disks on a very fast controller, and you will likely have better luck.

/Hoping this lesson is not lost ...

Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics Inc.
email: landman@xxxxxxxxxxxxxxxxxxxxxxx
web  : http://scalableinformatics.com
phone: +1 734 786 8423 x121
fax  : +1 866 888 3112
cell : +1 734 612 4615

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