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A new working group was established, including storage system developers
and managers, representatives from the experiments, and data-management
middleware developers. At the end of May the first version of SRM v2.2 was
agreed to. At the same time a WLCG-specific usage agreement (UA) spelled
out that WLCG client middleware would only exercise a subset of the full
functionality. This allowed the storage system developers to ignore features
not required by the UA or to postpone their implementation.
The new set of requirements essentially was the following:
Only permanent files; that is, only the user can remove files.
Advance space reservation without streaming, initially only static, later also
dynamic.
Quotas. Unfortunately not yet accepted as an SRM feature.
Permission functions with POSIX-like ACLs for directories and files. It must
be possible to match permissions to the contents of the client's proxy
credentials, that is, the distinguished name and/or a set of VOMS groups
and roles.
It must be possible for privileged users, groups, and roles to have a better
quality of service, for example, dedicated disk pools, higher priority.
Basic directory functions: mkdir; rmdir; rename (on the same SE); remove;
list (up to a server-dependent maximum number of entries may be re-
turned).
Data transfer control functions: stage-in and stage-out type functionality;
pinning and unpinning; request status monitoring; request cancellation.
Paths relative to an implicit VO-specific base directory.
Paths should be orthogonal to quality of service (e.g., retention policy, access
latency).
A method to discover the supported transfer protocols.
3.4.4.4
The Storage Classes
In the summer of 2006 the WLCG Storage Classes Working Group was es-
tablished to understand the requirements of the LHC experiments in terms of
quality of storage (storage classes) and how such requirements could be im-
plemented in the various storage solutions available. For instance, this implies
understanding how to assign disk pools for LAN or WAN access and trying
to devise common configurations for VOs and recipes tailored per site.
The storage class determines the essential quality-of-service properties that
a storage system needs to provide for given data.
The LHC experiments have asked for the availability of combinations of
the following storage devices: tapes (or other reliable storage systems, always
referred to as tape in what follows) and disks. A file residing on tape is said
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