A special class of resources are compound resources. These can be used to integrate HPSS, Amazon S3, FTP and ADS type storage solutions into iRODS. A compound resource is a class where the POSIX data access type I/O calls such as open, read, write, lseek, close, etc are not readily available. Instead, it uses put and get calls to transfer entire files. Examples of the compound resource class are FTP, gridFTP, the HPSS parallel I/O, Amazon S3 and UK’s ADS. The compound resource implementation in iRODS requires a cache class resource to be configured in the same resource group as the compound resource. Data stored in the compound resource cannot be accessed directly but through the cache resource with staging and synchronizing using the put/get driver functions.

Beside the standard resource types (like file system or HPSS) which can serve as back-end storages in compound resources there is a possibility to access special storage solutions. iRODS provides Universal Mass Storage System driver which can be used to implement access to such a special storage solution. iRODS installation provides a scaffold for a storage driver, it can be found in iRODS/server/bin/cmd/univMSSInterface.sh. Following (self-explanatory) methods must be implemented to integrate a storage into iRODS:

  • syncToArch ()
  • stageToCache ()
  • mkdir ()
  • chmod ()
  • rm ()
  • mv ()
  • stat ()

An example of Universal Mass Storage System driver is an implementation of dCache access provided by Robert Verkerk.

In order to use the driver, the admin has to create a cache resource and compound resource of "MSS universal driver" class with following commands:
mkdir /var/tmp/eudatCache iadmin mkresc eudatCache "unix file system" cache irods.grid.sara.nl /var/tmp/eudatCache iadmin modresc eudatCache comment "eudat cache storage" iadmin mkresc eudatPnfs 'MSS universal driver' compound irods.grid.sara.nl /pnfs/grid.sara.nl/data/irods/ iadmin modresc eudatPnfs comment "eudat pnfs storage" iadmin atrg eudat eudatCache iadmin atrg eudat eudatPnfs

 

It is, currently possible to access only one resource via Universal Mass Storage System driver per iRODS server.