n/w ram or DSM ??

Donald Becker becker at scyld.com
Fri Nov 22 00:48:20 PST 2002

On Fri, 22 Nov 2002, Anand Tiwari wrote:

> I want to start my thesis on the issues of cluster memory management. i am 
> interested in working on "Network RAM" and "DSM". i went through few
> papers and  i realized that at some point we always required "network ram". 

A better term is NVM -- Network Virtual Memory.

> Also i am pretty confused about network ram, is it a separate thing or its a 
> layer beneath "DSM". can anybody clear my doubt and give me some ideas about 
> where to start looking for some work.

Let's define the terms 

DSM implies synchronized, consistent access across a set of machines.
On a cluster that usually means a protocol that enforces a single
writer per native hardware VM page.  On custom hardware the
single-writer granularity a typically a cache line.

NVM implies using memory on remote machines as a high performance
backing store, with a much looser consistency model when there are
multiple writers.

The only DSM system that I have heard about recently is the venerable
'Treadmarks', which curiously seems to come up in conversation about a
once a week recently after DSM went almost unmentioned for years.

> i also feel that if we try to have severless ram ( or ram without any
> central controller) we can have better life.

Yup, but truly distributed resource managers seem to be much more
expensive than a centralized manager, or redundant-but-centralized
managers.  It's pretty much the same problem as distributed lock
managers (DLMs) on cluster file systems. Everyone wants a DLM on the
feature list, but the complexity is much lower and performance higher
with a centralized manager.

Donald Becker				becker at scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Scyld Beowulf cluster system
Annapolis MD 21403			410-990-9993

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