**5. AliEn**

AliEn [30] is a set of middleware tools and services which represents an implementation of the ALICE distributed computing environment integrated in the WLCG environment. AliEn has been under a constant development by ALICE since 2001 and was deployed over the ALICE Grid infrastructure right from the start. One of the important features is the set of interfaces to other Grid implementations like gLite [57], ARC [58] and OSG [17].

AliEn was initially developed as a distributed production environment for the simulation, reconstruction, and analysis of Physics data. Since it was put in the production in 2001, ALICE has been using AliEn before the start of the real data taking for distributed production cycles of Monte-Carlo simulated raw data, including subsequent reconstruction and analysis, during the regular Physics Data Challenges. Since 2005, AliEn has been used also for end-user analysis. Since December 2007, when the ALICE detector started operation taking cosmic data, AliEn has been used also for management of the raw data. Since the LHC startup in 2009, millions of jobs have been successfully processed using the AliEn services and tools.

AliEn developers provided the users with a client/interface - "alien shell" [59] and a set of plugins designed for the end users' job submission and handling. These tools together with the tools provided by the ALICE Grid monitoring framework MonALISA [44], hide the complexity and heterogenity of the underlying Grid services from the end-user while facing the rapid development of the Grid technologies.

AliEn is a lightweight Open Source Grid framework built around Open Source components using the combination of standard network protocols, a Web Service and Distributed Agent Model. The basic AliEn components include:


20 Will-be-set-by-IN-TECH

sites represent in excess of 20 thousands of CPUs, 12 PB of distributed disk storage and 30 PB of distributed tape storage, and the gradual upscale of this capacity is ongoing. Similar to other LHC experiments, about half of the CPU and disk resources is provided by the Tier-2 centers. For the year 2012, ALICE plans/requirements for computing resources within WLCG represent 211.7 of kHEP-SPEC06 CPU capacity, 38.8 PB of disk storage and 36.6 PB of tapes

The concept of the ALICE computing model was officially proposed in 2005. Since then, it has been used for massive Monte Carlo event productions, for end-user analysis and for the raw data management and processing. The strategy has been validated under heavy load during a series of Data Challenges and during the real data taking in 2010/2011. The model provides the required Grid functionality via a combination of the common Grid services offered on the WLCG resources and the ALICE-specific services from AliEn. Today's computing environments are anything but static. Fast development in Information Technologies, commodity hardware (hardware being constantly replaced and operating systems upgraded), Grid software and networking technologies inevitably boosted also further development of the ALICE computing model. One of the main effects is a transformation of the model from the strictly hierarchical Tier-like structure to a more loose scenario, a "cloud-like" solution.

AliEn [30] is a set of middleware tools and services which represents an implementation of the ALICE distributed computing environment integrated in the WLCG environment. AliEn has been under a constant development by ALICE since 2001 and was deployed over the ALICE Grid infrastructure right from the start. One of the important features is the set of interfaces

AliEn was initially developed as a distributed production environment for the simulation, reconstruction, and analysis of Physics data. Since it was put in the production in 2001, ALICE has been using AliEn before the start of the real data taking for distributed production cycles of Monte-Carlo simulated raw data, including subsequent reconstruction and analysis, during the regular Physics Data Challenges. Since 2005, AliEn has been used also for end-user analysis. Since December 2007, when the ALICE detector started operation taking cosmic data, AliEn has been used also for management of the raw data. Since the LHC startup in 2009, millions of jobs have been successfully processed using the AliEn services and tools. AliEn developers provided the users with a client/interface - "alien shell" [59] and a set of plugins designed for the end users' job submission and handling. These tools together with the tools provided by the ALICE Grid monitoring framework MonALISA [44], hide the complexity and heterogenity of the underlying Grid services from the end-user while facing

AliEn is a lightweight Open Source Grid framework built around Open Source components using the combination of standard network protocols, a Web Service and Distributed Agent

to other Grid implementations like gLite [57], ARC [58] and OSG [17].

the rapid development of the Grid technologies.

Model. The basic AliEn components include:

• AliEn File Catalogue with metadata capabilities

• Data management tools for data transfers and storage

[56].

**5. AliEn**

**4.8 Concluding remarks**


AliEn was primarily developed by ALICE, however it was adopted also by a couple of other Virtual Organizations like PANDA [60] and CBM [61].
