**5.5 Monitoring**

Since the AliEn Workload Management does not depend directly on sophisticated monitoring, no special monitoring tools were developed in AliEn. As the monitoring solution, ALICE has adopted and further developed the Java-based MonALISA framework [44] mentioned already in the previous section. The MonALISA system is designed as an ensemble of autonomous multithreaded, self-describing agent-based subsystems which are registered as dynamic services, and together can collect and process large amounts of information.

The collected monitoring information is published via Web Service for use by AliEn Optimizers or for visualization purposes. An extension of the network simulation code which is a part of MonALISA can provide a tool for optimization and understanding of the performance of the AliEn Grid system.

#### **5.6 Storage**

Experience with the performance of different types of storage managers shows that the most advanced storage solution is the native XRootD manager [37] described in section 3. It has been demonstrated that with all other parameters being equal (protocol access speed and security) the native XRootD storage clusters exhibit substantially higher stability and availability. The ALICE distributed system of native XRootD clusters is orchestrated by the global redirector which allows interacting with the complete storage pool as a unique storage. All storages are on WAN (Wide Area Network).
