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Link Groups

The PoolManager supports a type of objects called link groups. These link groups are used by the SRM SpaceManager to make reservations against space. Each link group corresponds to a number of dCache pools in the following way: A link group is a collection of links and each link points to a set of pools. Each link group knows about the size of its available space, which is the sum of all sizes of available space in all the pools included in this link group.

To create a new link group login to the Admin Interface and cd to the PoolManager.

(local) admin > cd PoolManager
(PoolManager) admin > psu create linkGroup <linkgroup>
(PoolManager) admin > psu addto linkGroup <linkgroup> <link>
(PoolManager) admin > save

With save the changes will be saved to the file /var/lib/dcache/config/poolmanager.conf.

Note

You can also edit the file /var/lib/dcache/config/poolmanager.conf to create a new link group. Please make sure that it already exists. Otherwise you will have to create it first via the Admin Interface by

(PoolManager) admin > save

Edit the file /var/lib/dcache/config/poolmanager.conf

psu create linkGroup <linkgroup>
psu addto linkGroup <linkgroup> <link>

After editing this file you will have to restart the domain which contains the PoolManager cell to apply the changes.

Note

Administrators will have to take care, that no pool is present in more than one link group.

Properties of space reservation The dCache administrator can specify a RetentionPolicy and an AccessLatency for the space reservation, where RetentionPolicy describes the quality of the storage service that will be provided for the data (files) stored in this space reservation and AccessLatency describes the availability of this data.

A link group has five boolean properties called replicaAllowed, outputAllowed, custodialAllowed, onlineAllowed and nearlineAllowed. The values of these properties (true or false) can be configured via the Admin Interface or directly in the file /var/lib/dcache/config/poolmanager.conf.

The link groups contained in a space reservation match the RetentionPolicy and the AccessLatency of the space reservation.

(PoolManager) admin > psu set linkGroup custodialAllowed <linkgroup> <true|false>
(PoolManager) admin > psu set linkGroup outputAllowed <linkgroup> <true|false>
(PoolManager) admin > psu set linkGroup replicaAllowed <linkgroup> <true|false>
(PoolManager) admin > psu set linkGroup onlineAllowed <linkgroup> <true|false>
(PoolManager) admin > psu set linkGroup nearlineAllowed <linkgroup> <true|false>

Moreover an attribute can be assigned to a link group.

(PoolManager) admin > psu set linkGroup attribute <linkgroup> <key>=<value>

Example:

Possible assignments for attributes are:
(PoolManager) admin > psu set linkGroup attribute name-of-LinkGroup VO=dteam001
(PoolManager) admin > psu set linkGroup attribute name-of-LinkGroup VO=cms001
(PoolManager) admin > psu set linkGroup attribute name-of-LinkGroup HSM=osm

Note

Please note that that it is up to administrators that the link groups’ attributes are specified correctly.

For example dCache will not complain if the link group that does not support tape backend will be declared as one that supports custodial.