Grid Storage

Access to Grid Storage provided by the EGI HTC providers

Grid Storage

Grid Storage allows you to store data in a reliable and high-quality environment and share it across distributed teams. Your data can be accessed through different protocols and can be replicated across different providers to increase fault-tolerance. Grid Storage gives you complete control over the data you share and with whom. Main features:

  • Access highly-scalable storage from anywhere
  • Control the data you share
  • Organise your data using a flexible hierarchical structure

Grid Storage file access is based on gridFTP and WebDav/HTTP protocols together with XRootD and legacy SRM (under deprecation at some of the endpoints).

Several Grid storage implementation are available on the infrastructure, the most common are the following:

Endpoint Discovery

The Storage endpoints that are available to user’s Virtual Organizations are discoverable via the EGI Information System (BDII).

The lcg-infosites command can be used to obtain VO-specific information on existing grid storages

The syntax is the following:

lcg-infosites --vo voname -[v] -f [site name] [option(s)] [-h| --help]
  [--is BDII]

For example, to list the Storage Elements (SEs) available to the biomed VO one could issue the following command:

lcg-infosites --vo biomed  se

lcg-infosites --vo biomed  se
 Avail Space(kB)  Used Space(kB)  Type  SE
    280375465082             n.a  SRM
     10995116266              11  SRM

Client access

The access via client requires the user to obtain a valid X.509 user VOMS proxy. Please refer to the Check-in doc for more information. Integration with OpenID Connect and the EGI Check-in service is under piloting at some of the endpoints on the infrastructure , but it has not yet reached the production stage.

The client widely used to access grid-storage is gfal2 which is available for installation both on RHEL and Debian compatible systems.

In particular, gfal2 provides and abstraction layer on top of several storage protocols (XRootD, WebDAV, SRM, gsiftp, etc) and therefore is quite convenient as the same API can be used to access different protocols.

The gfal2 CLI can be installed as follows (for RHEL compatible systems):

yum install gfal2-util gfal2-all

where gfal2-all will install all the plug-ins to deal with all the available protocols.

In the following example the command to access storages via gfal2 are documented. Please note that the access via gsiftp protocol in the following example can be replaced by any other supported protocols

List files on a given endpoint:

gfal-ls gsi

Create a folder:

gfal-mkdir gsi

Copy a local file:

gfal-copy test.json gsi
Copying file:///root/Documents/test.json   [DONE]  after 0s

Copy files between storages:

gfal-copy gsi gsi
Copying gsi   [DONE]  after 3s

Download a file to a local folder:

gfal-copy gsi /tmp
Copying gsi   [DONE]  after 0s

Delete a file:

gfal-rm gsi
gsi      DELETED

More commands are available, please refer to the gfal2-util documentation

Access via the EGI Data Transfer service

The EGI Data Transfer service provides mechanism to optimize the transfer of files between EGI Online storage endpoints. Both a graphical interface and CLI are available to perform bulk movement of data. Please check the related documentation for more information.

Integration with Data Management frameworks

Grid Storage access most of the time is hidden to users by the integration performed within the Data Management framework used by Collaborations and Experiments.

In EGI for instance, the EGI Workload Management System EGI Workload Manager, provides a way to efficiently access grid storage endpoints in order to read and store files on the infrastructures and to catalogue the existing file and related location.

The users when running computation via DIRAC does not actually access the storage directly, but they can of course retrieve the output of the computation which has been stored by the system on the grid.

Last modified January 11, 2021: Fix linter issues (#172) (2219631)