[Go-essp-tech] Non-DRS File structure at data nodes

[stephen.pascoe at stfc.ac.uk]

Dear all,

I feel we've been through this argument many times before.  I have a few thoughts to add below ...

* I appreciate Gavin's argument assuming all indirection software is in place.  The problem is it isn't.  We already have people using the system and expecting some sort of uniformity of interface.  The HelpDesk has been asked several times about how to write generic web scripts, crawlers, or anything that would help them keep up to date on the data without continually browsing the Gateways.  A consistent URL structure is one think we said we'd give users.  This can be done with the current stack if you put your data in DRS structure, although much more could be done to make data access easier to script.

* The QC tool was developed assuming the DRS directory structure on disk -- no HTTP middleware is going to help in this case.  I believe this was a communication failure, pure and simple.  Developers at DKRZ believed they could rely on the DRS directory structure and they can't.  We need to do better communicating our policy.

* I generally agree with Gavin technically but I notice he doesn't mention end-user once.  It is clear that his target users are ESGF developers and deployers, not scientists wanting data services.  That's fine: Gavin's role is thinking ahead about the architecture but, at this stage, CMIP5 user requirements should be the priority of ESGF development as a whole.  Without that, some of us are going to spend most of the next year fighting fires and helping frustrated users with an unusable system.

* I'm sure the DRS in it's current form won't fit everyone's future metadata needs and so I'm not arguing the datanode should be forced to publish DRS structured data, just that we publish CMIP5 data in this structure.  One day there is a much wider debate to be had about whether the details of DRS are right.

* I sincerely hope we can explore torrents and torrent-like technology in ExArch.

Cheers,
Stephen.

---
Stephen Pascoe  +44 (0)1235 445980
Centre of Environmental Data Archival
STFC Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, UK

From: go-essp-tech-bounces at ucar.edu [mailto:go-essp-tech-bounces at ucar.edu] On Behalf Of Gavin M. Bell
Sent: 02 September 2011 20:25
To: V. Balaji
Cc: go-essp-tech at ucar.edu; Luca Cinquini; esg-node-dev at lists.llnl.gov; Laura Carriere
Subject: Re: [Go-essp-tech] Non-DRS File structure at data nodes

Hi Balaji,

Indeed you have good points.  The only thing I am suggesting is that it is an equally daunting task to *impose* anything on a group of people.  I am a big fan of the benevolent dictatorship, but as history tells us, they don't last.  I guess I would contend that having a transparent, open, easy to grok algorithm would be incumbent upon any institution that decides to take advantage of such an indirection mechanism.  It is optional.  It may very well be for a community as disciplined as the climate community (I am quite serious many other communities look to the climate community as  model of organization) that having a single structure would suffice.  But from a system admin perspective filesystem requirements may be prohibitive.  As we can see just from this discussion, many are already looking for ways to perform this indirection.  I propose that we allow this indirection in a regimented way so we can all understand / embrace the mechanism by which this is done.  Think of it like a well known hashing algorithm that we know how to plug into to get out what we want.  As long as the transformation machinery is clear then the particular transform becomes a simpler, more circumscribed task.  I only propose that we allow for this at the highest ingress level... ESGF.  This ameliorates the burden on ESGF.  Let's not forget ESGF belongs to all of us, *we* are *them*.

As for torrents... well, in my mind's eye that is what we are building to some extent, but with better security that avoids some of the byzantine attacks torrents are prone to.  ESGF should have the best features from that community... at least that's part of the goal of the design.  Oh, and ESGF won't preclude using torrents... as a matter of fact you could create a back-end that is a true torrent in/egress that plugs into ESGF... Oh... but then you will need a transformation layer to allow that to happen, it would be nice to have one available to plug into, right? ;-).

On 9/2/11 11:53 AM, V. Balaji wrote:

I've been a proponent since the beginning of having a file layout

(DRS) agreed by convention and _imposed_ (rather than recommended)

on participant nodes. While this may be old-fashioned thinking,

our finding is that predictable paths are the most useful thing for

building the software, and I continue to believe that it's not so

difficult to agree upon a file layout. I think the difficulties here

arose from a discrepancy in the way DRSlib and CMOR handled versioning

rather than people digging their heels in about a conventionally

agreed file and directory layout.



Regarding Gavin's larger point, having an indirection layer in the

middleware separating the apparent path in the query from the actual

path in the resource introduces a huge dependency on that indirection

layer: pretty much nothing can function without it. I'm not sure ESGF

should take upon itself such a huge burden.



With DRS being an imposed convention, you could undertake many tasks

following software paths for which we aren't responsible. There are

many tasks -- e.g data movement, replication -- which are shared by

communities much larger than ESGF and shouldn't require specialized

middleware. One of my big disappointments is that we don't use torrents

for anything:-).



Gavin M. Bell writes:



Hi Estani and colleagues, :-)



Okay, so let me jump in for a minute.  There are two notions that are

being conflated in this discussion.  Everyone is used to using paths and

such to find things on the filesystem.  Also people are used to using

tried and true mechanisms that use the filesystem to get to information

remotely by further qualifying the filesystem path with the host.  This

is all well and good for the scope of these tools.



Now we are in a distributed world as we build this ESG*F* (Federation)

that will unify and sew together disparate organizations' data into a

seamless 'dataspace'.  The goal of building such a thing is to make it

easy for all interested in the data to get to data and post data and in

so doing share data in an environment that is fluid.



ESGF is providing a mechanism/platform/infrastructure... that

simultaneously addresses the need for everyone to share data while

maintaining sovereign custody over their data assets.  ESGF has already

met this challenge in many ways.  However, to continue to make the

system simple and easy to use and a joy to use we should alleviate the

requirement of filesystem structure.  This is a particular case where

'some' is good but 'too much' hurts.



So now, cutting to the chase.  More than anecdotal evidence (the length

of this discussion) clearly suggests that strict filesystem adherence is

not in accord with the sovereignty we would like organizations to

enjoy.  It would behoove us to operate the federation such that

descriptors in the context of the federation are divorced from

filesystem structure itself.  This can be achieved rather directly.



Going back to what I initially said, the two notions being conflated

here are the *query* and the *resource*.  An URL, even the filesystem

path itself, is nothing more than a query to the network/operating

system to locate bits on a platter (clearly I am dating myself).  We

should use the DRS as the Federation's canonical locator for resources.

The DRS is the *query* (in the same spirit as above).  The ESGF system,

just like the filesystem, would resolve the query (DRS) to the

resource.  This, by the way, bears fruit in quite few places in the

system making quite few things more efficient.



I have thought about this particular filesystem problem and have come up

with a solution... the solution would allow us to still use tools like

wget/curl right out of the box and with a little bit of tweaking gridftp

and globus.  As a matter of fact the solution would lend itself to being

used by any tool old or new.  To more directly address Estani's

questions about *relying* on things.... I don't think that the tone of

that should be so pejorative.  You *use* a tool because it helps you. I

feel that using the ESGF infrastructure is useful to the community and

the communities goals.  I don't think that it is too much skin in the

game to ask for.  If things go horribly wrong, your organization has

it's own filesystem structure that fits their needs that they can rely

on in order to make sense of things as they see it.  So, fundamentally

the act of scanning the data is what provides the cohesion between the

DRS and filesystem structure.  The job of scanning is certainly not

terribly laborious.  So there is quite literally very *little* cost to

"relying" on a system/infrastructure/set of tools that is ESGF,

especially compared to the benefit of what ESGF can bring to this

community. I find it hard to conjure a cogent argument against creating

a flexible system, especially given the nature of this

multi-organization, international effort. We must make it easy for

organizations to be independent and not push a myopic view (IMHO) of a

certain state of the world on everyone.



Thank you for reading this rather lengthy email... I need an in-house

editor perhaps... I tend to get garrulous but I wanted to be as clear as

I could.



If there isn't already a working group on this I would like to propose

one, we can set it up on the ESGF wiki and talk more about this.  :-)



P.S.

In 10 years ESGF will have morphed into something even more lovely...

because it is build by the all of us and nurtured on our wisdom :-).

The will be the tool people count on and rely on as you alluded to with

ftp, et. al.  There is no tomorrow without today (modulo the quantum

mechanics fridge).



On 9/2/11 2:55 AM, Estanislao Gonzalez wrote:

I know the main idea is to create a middleware layer that would make

file structures obsolete. But then, we will have to write all tools

again in order to interact with this intermediate level or at least

patch them somehow. gridFTP, as well as ftp, are only useful as

transmission protocols, you can't write your own script to use them,

you have to rely on either the gateway or the datanode to find what

you are looking.

In my opinion, we will be relying too much in the ESG infrastructure.

What would happen if we loose the publisher database? How would we

tell apart one version from another, if this is not represented in the

directory structure?

My fear is that if we keep separating the metadata from the data

itself, we add a new weak link in the chain. Now if we loose the

metadata the data will also be useless (this would be indeed the worst

case scenario). In 10 years we will have no idea what this interfaces

were like, probably both data node and gateways will be superseded  by

newer versions that can't translate our old requirements. But as I

said, that's a problem for LTAs only. In any case, we need the

middleware to provide some services and speed things up, but I don't

think we should rely blindly on it.









--

Gavin M. Bell

--



 "Never mistake a clear view for a short distance."

               -Paul Saffo



-- 
Scanned by iCritical.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.ucar.edu/pipermail/go-essp-tech/attachments/20110905/cd46a333/attachment-0001.html