Hi Jens,
thanks for the explanation.
Where bob and alice would fit in the tier1 architecture 2nd or 3rd layer?
How the dcache head node enters in the transfers? Does it act only as a
location/acls database that needs to be updated when the transfer is
complete?
cheers
alessandra
On Tue, 22 Feb 2005, Jensen, J (Jens) wrote:
>>> I think everything is correct. Only addition is that the
>> difference between
>>> CMS and the data challenge is that CMS do srmcp's where as
>> the service
>>> challenge does a (get-turl && get-turl) , 3rd party g-u-c,
>>> (close-turl && close-turl). This is why the disk servers
>> them selves
>>> must be exposed to internet in the CMS case since it is
>> them that do the
>>> transfer for you and they do it non-passivly.
>>
>> what package does srmcp belong?
>> what package do get-turl/3rd party g-u-c/close-turl belong?
>> what does g-u-c mean?
>> what is the difference between the two?
>>
>
> Just to clarify third party copying, in this context.
>
> One difference is when you're doing 3rd party copying - from one
> remote SRM (call it Alice) to another (call it Bob).
>
> There's an SRMCopy command. You tell Alice to transfer the file
> to Bob. Alice does a 'put' to Bob, opens a GridFTP channel to
> Bob and uploads the file, then commits it (status -> done).
> You don't need to access Bob, you only need to be able to talk
> to Alice.
>
> SRMCopy (function call, as opposed to srmcp client tool) is in
> SRM1.1 but not in 1.0. That's just another reason why at least
> parts of the spec for SRMCopy are open to interpretation :-)
>
> Then there's the other way. You do a 'get' from Alice and a
> 'put' to Bob. This gives you two TURLs. Then you do a GridFTP
> 3rd party transfer - transfer from one remote TURL to another.
> Then you close the files (setting status to Done again).
>
> The data in both cases goes from Alice to Bob, not to yourself.
>
> And the g-u-c is globus-url-copy which is the GridFTP client
> doing the actual transfer from Alice to Bob.
>
> The difference is not invoking SRMCopy to do the transfer but
> doing it manually. As I mentioned, SRMCopy is not really that
> well defined - plus it requires delegated credentials (yours,
> delegated to Alice), so it's perhaps best avoided.
>
> Cheers,
> --jens
>
--
********************************************
* Dr Alessandra Forti *
* Technical Coordinator - NorthGrid Tier2 *
* http://www.hep.man.ac.uk/u/aforti *
********************************************
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