Scalable and cost-effective Storage Elements are essential components of Grid systems. An increasing number of data-intensive applications and services in Grids make the cost-effective scalability of capacity and performance of the storage infrastructure a very hot research topic. In this paper, we present the practical evaluation of the performance features of two classes of storage systems. We tested an example custom technology-based storage system, the FC-SATA disk matrix and a commodity-based storage solution, the Violin system, developed at FORTH. Using a block-level benchmark, we examined the performance limits and the scalability features of both classes of systems.