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Configuring pools to interact with a Tertiary Storage System
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The dCache Book > Configuration of dCache > The dCache Tertiary Storage System Interface > Configuring pools to interact with a Tertiary Storage System

Configuring pools to interact with a Tertiary Storage System

The executable interacting with the Tertiary Storage System (TSS), as described in the chapter above, has to be provided to dCache on all pools connected to the TSS. The executable, either a script or a binary, has to be made “executable” for the user, dCache is running as, on that host.

The following files have to be modified to allow dCache to interact with the TSS.

  • The /var/lib/dcache/config/poolmanager.conf file (one per system)
  • The pool layout file (one per pool host)
  • The pool 'setup' file (one per pool)
  • The namespaceDomain layout file (one per system)

After the layout files and the various ’setup’ files have been corrected, the following domains have to be restarted :

  • pool services
  • dCacheDomain
  • namespaceDomain

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The dCache layout files

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The /var/lib/dcache/config/poolmanager.conf file

To be able to read a file from the tape in case the cached file has been deleted from all pools, enable the restore-option. The best way to do this is to log in to the Admin Interface and run the following commands: 

[example.dcache.org] (local) admin > cd PoolManager
[example.dcache.org] (PoolManager) admin > pm set -stage-allowed=yes
[example.dcache.org] (PoolManager) admin > save

A restart of the dCacheDomain is not necessary in this case.

Alternatively, if the file /var/lib/dcache/config/poolmanager.conf already exists then you can add the entry 

pm set -stage allowed=yes

and restart the dCacheDomain.

Warning

Do not create the file /var/lib/dcache/config/poolmanager.conf with this single entry! This will result in an error.

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The pool layout

The dCache layout file must be modified for each pool node connected to a TSS. If your pool nodes have been configured correctly to work without TSS, you will find the entry lfs=precious in the layout file (that is located in /etc/dcache/layouts and in the file /etc/dcache/dcache.conf respectively) for each pool service. This entry is a disk-only-option and has to be removed for each pool which should be connected to a TSS. This will default the lfs parameter to hsm which is exactly what we need.

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The pool ’setup’ file

The pool ’setup’ file is the file $poolHomeDir/$poolName/setup. It mainly defines 3 details related to TSS connectivity.

  • Pointer to the executable which is launched on storing and fetching files.
  • The maximum number of concurrent STORE FILE requests allowed per pool.
  • The maximum number of concurrent FETCH FILE requests allowed per pool.

Define the executable and Set the maximum number of concurrent PUT and GET operations: 

hsm set <hsmType> [<hsmInstanceName>] [-command=</path/to/executable>] [-key=<value>]

#
#  PUT operations
# set the maximum number of active PUT operations >= 1
#
st set max active <numberOfConcurrentPUTS>

#
# GET operations
# set the maximum number of active GET operations >= 1
#
rh set max active <numberOfConcurrentGETs>
  • <hsmType>: the type ot the TSS system. Must be set to “osm” for basic setups.
  • <hsmInstanceName>: the instance name of the TSS system. Must be set to “osm” for basic setups.
  • </path/to/executable>: the full path to the executable which should be launched for each TSS operation.

Setting the maximum number of concurrent PUT and GET operations.

Both numbers must be non zero to allow the pool to perform transfers.

Example:

We provide a script to simulate a connection to a TSS. To use this script place it in the directory /usr/share/dcache/lib, and create a directory to simulate the base of the TSS. 

[root] # mkdir -p /hsmTape/data

Login to the Admin Interface to change the entry of the pool ’setup’ file for a pool named pool_1. 

(local) admin > cd pool_1
(pool_1) admin > hsm set osm osm
(pool_1) admin > hsm set osm -command=/usr/share/dcache/lib/hsmscript.sh
(pool_1) admin > hsm set osm -hsmBase=/hsmTape
(pool_1) admin > st set max active 5
(pool_1) admin > rh set max active 5
(pool_1) admin > save

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The namespace layout

In order to allow dCache to remove files from attached TSSes, the “cleaner.enable.hsm = true” must be added immediately underneath the [namespaceDomain/cleaner] service declaration: 

[namespaceDomain]
 ... other services ...
[namespaceDomain/cleaner]
cleaner.enable.hsm = true
.. more ...

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What happens next

After restarting the necessary dCache domains, pools, already containing files, will start transferring them into the TSS as those files only have a disk copy so far. The number of transfers is determined by the configuration in the pool ’setup’ file as described above in the section called “The pool ’setup’ file”.

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