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Post by Yancy Hollis with Palo Alto IT Pro Group and Coders
The use of virtualization and multi-core processors has made cloud computing an option for many
users.
The ability to buy cloud time as you need it and not purchase hardware is certainly attractive
from a financial standpoint.
The concept is not new and has its roots in time shared mainframes and grid computing.
One might assume the the vast amount of computing
resources in clouds may make them ideal candidates for HPC (high performance computing) clustering. Unfortunately, it is not
as simple as collecting cores.......
One of the issues facing clouds is I/O. Basically, I/O is often not predictable
or repeatable. From a storage standpoint read and write times can be fast, but not always fast. In terms of messages between
servers, most clouds do not support high performance interconnects and similarly make no guarantees as to latency or bandwidth
consistency. While grids paid attention to certain HPC performance guarantees in terms of I/O, clouds, in order to offer ease
of use, have declined such guarantees.
Unless a cloud has been specifically designed for HPC, the user cannot
expect consistent and/or high performance. There are two papers which discuss this very idea.
The first paper
looks at Benchmarking Amazon
EC2 for High-performance Scientific Computing and the second paper asks, Can Cloud Computing Reach The TOP500?. Both papers conclude that the cloud is not mature enough for HPC (high performance computing) applications.
The limitations
of the cloud become more apparent when one looks a little deeper at HPC applications. First, many applications rely on user
space communication (i.e. high performance MPI programs transfer data directly from one node to another without using
kernel services.)
Such a close to the wire operation runs counter to the virtualization model. Secondly,
as reported in the first paper (above), the performance of OpenMP applications was reduced by 7-21% when running in the EC2
cloud.
cloud-cluster-diagram
Recently Penguin
Computing began offering POD (Penguin on Demand) for HPC cloud computing.
The POD cloud offers both Ethernet and InfiniBand connections between nodes thus providing a dedicated high performance computing
environment. This service can be considered a specialized HPC cloud.
There are some other other important issues to consider with cloud
computing -- security and reliability.
When data leaves your domain over the Internet it is virtually impossible
to guarantee 100% security. If your organization can live with this situation, using the cloud may be an option. If on the
other hand, you need to keep a tight reign on your data, then you may not want to be injecting it into the cloud.
The other issue is reliability. If your day to day operations are based on using a cloud, then a contingency plan is a must.
Interruptions in Internet traffic due to congestion or hardware failures can be common in some areas. In addition,
the cloud provider may have issues (even go out of business) and thus not meet the service requirements.
I believe the cloud is an interesting
model, but it is not a real solution for HPC (in its current form).
My issue with clouds is that they are often
categorized as "grid like" and then are somehow (incorrectly) considered "HPC like." Cloud offers utility
computing like grid promised, but has pushed the application layer further away from the hardware.
HPC practitioners
spend a lot of time making sure the application is as close to the hardware as possible. At this point in time, HPC in the
cloud is more of a curiosity than a solution. When examining HPC benchmarks it becomes clear that clouds are not the best
means to provide HPC cycles.
Whether efforts like POD can meet the HPC users needs in the cloud is still unknown.
cloud-cloud-ms
To be fair,
there are some HPC applications that lend themselves to clouds quite well. Keep in mind they have been designed to work in a robust distributed fashion
and are not virtualized. Clouds can be enticing and even enabling for some applications, but remember a collection of servers
(in the cloud or in a rack) does not a cluster make.....................
