[glue-wg] RetentionPolicy definitions

[Maarten.Litmaath at cern.ch]

Ciao Sergio,

> ExpirationMode and its values

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The Expiration Modes of a container indicate if it supports files
with infinite and/or finite lifetimes, and what actions the storage
system may take upon the expiration of a file.

The value NeverExpire indicates support for files with infinite lifetime:
they can only be removed by authorized clients, not by the storage system
itself.

The value WarnWhenExpired indicates support for files that have finite
lifetimes, but on expiration cannot be removed by the storage system
itself.  The data content of an expired file may be deleted if it can
be recovered from an archive.  New store operations may fail for certain
clients until (some of the) expired files have either been removed by
authorized clients, or have had their lifetimes increased.

The value ReleaseWhenExpired indicates support for files that have
finite lifetimes and on expiration will be removed by the storage system.

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> AccessLatency and its values

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The Access Latency of a container indicates the maximum latency for
a file stored in that container to be made available for reading.

The latency ONLINE indicates that files are always on disk,
hence cannot have their latency improved.

The latency NEARLINE indicates that a file may have its only copies
in a "nearly online" component of the storage system, typically
a fully automated tape robot, but also a remote storage system
could fit this qualification.  Such a facility will need an
unspecified amount of time to make a copy of the file available
on the disk component of the container under consideration.
When a file is not in use, its disk copies may be removed.
Hence the system cannot guarantee that a file will be immediately
available on disk.

The latency OFFLINE indicates that a file may have its only copies
in an offline component of the storage system, for example a tape
library that is not connected to an automated tape robot.  Hence
an operator intervention may be needed to make a copy of a file
available that has a lower latency.
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