Distributed Virtual Disks

Distributed Virtual Disks

Introduction:

The ideal storage system is globally accessible, always available, provides unlimited performance and capacity for a large number of clients, and requires no management. It is conventionally believed that nothing is ideal in the universe. But still, if one tries to incorporate majority of these features in a single system, then a cost-effective scalable system becomes available. As mentioned earlier the ideal storage system is always available and is incrementally expandable. Existing storage systems are far from this ideal. The recent introduction of low-cost, scalable, high-performance networks allows us to re-examine the way we build storage systems and to investigate storage architectures that bring us closer to the ideal storage system. Petal, attempts to approximate this ideal in practice through a novel combination of features.
Currently, managing large storage systems is an expensive and complicated process. Various estimates suggest that for $1 of storage $5-$10 is spent to manage it. Adding a new storage device frequently requires a dozen or more distinct steps, many of which require reasoning about the system as a whole and are, therefore, difficult to automate. Often a single component failure can halt the entire system, and requires considerable time and effort to resume operation. For instance, in a network using a ring topology or a star topology, the hub acts like a server through which all the transactions occur. Thus, hub is a single element whose failure may result in a system halt. Moreover, the capacity and performance of individual components in the system must be periodically monitored and equipoised to reduce fragmentation and elimination of hot spots. This usually requires a lot of manual work in moving, partitioning, or replicating files and directories. Replicating of data blatantly increases the space complexity of the system. The ultimate solution to overcome all these problems is, Petal, a cost-effective scalable network that is an easy-to-manage distributed storage system.
Petal consists of a collection of network connected servers that cooperatively manage a pool of physical disks. To a Petal client, this collection appears as a highly available block-level storage system that provides large abstract containers called virtual disks. A virtual disk is globally accessible to all Petal clients on the network. A client can create a virtual disk on demand to tap the entire capacity and performance of the underlying physical resources. Furthermore, additional resources, such as servers and disks, can be automatically incorporated into Petal.


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