[Beowulf] Hadoop

Jeff Layton laytonjb at att.net
Sat Dec 27 09:35:41 EST 2008


Sorry for top-posting (I hate these on-line email tools...)

Did the person requesting Hadoop ever say why they wanted it? For example, do they have code written in MapReduce or do they think that Hadoop will give them faster throughput than something else?

Hadoop is a project that really has 2 parts to it - an open-source MapReduce implementation, and a file system. From people I've talked to, the MapReduce part is used far more than the file system. But I've talked to some of the developers of the file system and there are some people who use the file system.

In general the file system is basically a virtual file system ala' PVFS, GlusterFS or any object based storage (Panasas, Lustre). However it understand the idea of locality - that is where useful storage is in relation to the compute part of the problem. The idea being that you can reduce the time to transmit the data because the storage is closer. But, in general, the improvement you get is due to the network topology, not necessarily the file system itself. That's because, in general, MapReduce systems have network topologies with bottlenecks all over the place because they don't really need a full bi-sectional bandwidth network everywhere. So for example they may have good bandwidth to a switch within the rack, but outside the rack, they bandwidth is not so hot. But again, these are generalizations, and the details are always in the implementation.

HadoopFS (lack of a better phrase on my part) is really designed for MapReduce codes - transactional codes. So if the person's code(s) fit this model, then it might be an interesting experiment to try. Otherwise, there are much better file systems for HPC :)

BTW - I saw Karen's post about using Java with HadoopFS. Be sure to pay attention to that since getting a good 64-bit Java implementation for Linux is not always easy. There are a few out there (Sun has an early access program to a 64-bit Java) but the reports I've heard are that it's still early.

Hope this helps.

Jeff





________________________________
From: Gerry Creager <gerry.creager at tamu.edu>
To: Beowulf Mailing List <beowulf at beowulf.org>
Sent: Friday, December 26, 2008 6:16:04 PM
Subject: [Beowulf] Hadoop

The subject line says it all: Hadoop:  Anyone got any experience with it 
on clusters (OK, so Google does, but that really wasn't the question, 
was it?).

We've a user who has requested its installation on one of our clusters, 
a high-throughput system.  I'm a bit concerned that it's not gonna be 
real compatible with, say, Torque/Maui and Gluster, unless we were to 
install Xen across the whole cluster and instantiate it within Xen VMs.

However, before I push all MY fears out into the discussion I'd prefer 
to see if anyone else has experience and can shed light on compatibility.

Thanks, Gerry
-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University    
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843
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