Create a sym link in EOS namespace for tape data

1

Hi,

SNOPLUS, a small high energy physics VO based in Canada, would like to recall ~200TB of tape data from RAL. The VO’s top-level dir in the EOS namespace is “/eos/antares/prod/snoplus”.

However, the data management system that will be used for this purpose, DIRAC, cannot cope with the abbreviated VO name “snoplus” and it expects (hard-coded) the full VO name “snoplus.snolab.ca”

My question: is it possible to create a symbolink link like for example
/eos/antares/prod/snoplus/ → /eos/antares/prod/snoplus.snolab.ca/

From docs - file — EOS CITRINE documentation - it looks like that this can be done only on a file by file basis but I am not sure.

Can you please confirm? And, is there any danger for the tape data from this change?

Thanks,

George

2

Hi George,
you can use the mapping mechanism of EOS for this mapping the long domain to the short one:

eos map
'[eos] map ..' provides a namespace mapping interface for directories in EOS.
Usage: map [OPTIONS] ls|link|unlink ...
Options:
map ls :
                                                : list all defined mappings
map link <source-path> <destination-path> :
                                                : create a symbolic link from source-path to destination-path
map unlink <source-path> :
                                                : remove symbolic link from source-path
3

You can also use symlinks for directories …

4

Thanks Andreas.

I will have a go with the “eos map”.

Sorry for the stupid question: is this safe for the tape files? Tape files (as disk replicas I suppose) have fxids which somehow encode the full path (or only the file?)

George

5

This has no impact, that is safe!

Internally you adress everything by id.

6

Thanks for the confirmation. How exactly the EOS mapping is supposed to work?

I have created an empty dir that will be the link

eos mkdir /eos/antarespreprodfac/factest.rl.ac.uk/

I mapped the real dir to the link

eos map link /eos/antarespreprodfac/factest/ /eos/antarespreprodfac/factest.rl.ac.uk/

I can see the link

eos map ls
/eos/antarespreprodfac/factest/ => /eos/antarespreprodfac/factest.rl.ac.uk/

However, the files in the “real” dir apprear to be gone…they dont appear when trying to do

eos ls -l /eos/antarespreprodfac/factest/

They appear again when the mapping is removed.

Can you please clarify?

George

7

You have to inverse the mapping! You map the existing files away into the empty directory!

8

Many thanks Andreas, this mapping

/eos/antarespreprodfac/factest.rl.ac.uk/ => /eos/antarespreprodfac/factest/

indeed worked as expected (even for tape files!)

George