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

[V. Balaji]

It would be great if the URL-to-path translation were a simple hash,
but in actual fact it's a THREDDS aggregation layer:-).

I could be wrong, but I've not seen enough to convince me that this
can scale up to the demands likely to be placed up it for CMIP5. Recall
that our data volumes are such that people are likely to make a lot
of server-side queries before they can configure a minimal hyperslab
to download for each of their science problems.

Gavin M. Bell writes:

> 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.
>>>
>
>

-- 

V. Balaji                               Office:  +1-609-452-6516
Head, Modeling Systems Group, GFDL      Home:    +1-212-253-6662
Princeton University                    Email: v.balaji at noaa.gov