Free Tutors the snia shared storage model Graphical representations An elementary overview and The components

Free Tutors the snia shared storage model  Graphical representations An elementary overview and The components

The SNIA Shared Storage Model further defines how storage architectures can be graphically illustrated. Physical components are always represented as three-dimensional objects, whilst functional units should be drawn in two-dimensional form. The model itself also defines various colours for the representation of individual component classes. In the black and white format of the book, we have imitated these using shades of grey. A coloured version of the illustrations to this chapter can be found on our home page Thick lines in the model represent the data transfer,

whereas thin lines represent the metadata flow between the components.

 An elementary overview

The SNIA Shared Storage Model first of all defines four elementary parts of a shared storage environment (Figure 10.1):

1. File/record layer The file/record layer is made up of database and file system.

2. Block layer The block layer encompasses the storage devices and the block aggregation. The SNIA Shared Storage Model uses the term 'aggregation' instead of the often ambiguously used term 'storage virtualization'. In Chapter 5, however, we used the term 'storage virtualization' to mean the same thing as 'aggregation' in the SNIA model, in order to avoid ambiguity.

3. Services subsystem The functions for the management of the other components are defined in the services subsystem.

4. Applications Applications are not discussed further by the model. They will be viewed as users o the model in the widest sense.

 The components

The SNIA Shared Storage Model defines the following components:

• Interconnection network The interconnection network represents the storage network, i.e. the infrastructure, that connects the individual elements of a shared storage environment with one another. The interconnection network can be used exclusively for storage access, but it can

also be used for other communication services. Our definition of a storage network (Section 1.2) is thus narrower than the dentitions of the interconnection network in the SNIA model. The network must always provide a high-performance and easily scalable connection for the shared storage environment. In this context, the structure of the interconnection network – for example redundant data paths between two components to increase fault-tolerance – remains just as open as the network techniques used. It is therefore a prerequisite of the model that the components of the shared storage environment are connected over a network without any definite communication protocols or transmission techniques being specified.

In actual architectures or installations, Fibre Channel, Fast Ethernet, Gigabit Ethernet, InfiniBand and many other transmission techniques are used (Chapter 3). Communication protocols such as SCSI, Fibre Channel FCP, TCP/IP, RDMA, CIFS or NFS are based upon these.

• Host computer Host computer is the term used for computer systems that draw at least some of their storage from the shared storage environment. According to SNIA, these systems were often omitted from classical descriptive approaches and not viewed as part of the environment. The SNIA shared storage model, however, views these systems as part of the entire shared storage environment because storage-related functions can be implemented on them. Host computers are connected to the storage network via host bus adapters or network

cards, which are operated by means of their own drivers and software. Drivers and software are thus taken into account in the SNIA Shared Storage Model. Host computers can be operated fully independently of one another or they can work on the resources of the storage network in a compound, for example, a cluster

• Physical storage resource All further elements that are connected to the storage network and are not host computers are known by the term 'physical storage resource'. This includes simple hard disk drives, disk arrays, disk subsystems and controllers plus tape drives and tape libraries. Physical storage resources are protected against failures by means of redundant data paths (Section 6.3.1), replication functions such as snapshots and mirroring (Section 2.7) and RAID (Section 2.5).

\• Storage device A storage device is a special physical storage resource that stores data.

• Logical storage resource The term 'logical storage resource' is used to mean services or abstract compositions of physical storage resources, storage management functions or a combination of these. Typical examples are volumes, files and data movers.

• Storage management functions The term 'storage management function' is used to mean the class of services that monitor and check (Chapter 8) the shared storage environment or implement logical storage resources. These functions are typically implemented by software on physical

storage resources or host computers.