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Diskless nodes (or computers acting as such) are sometimes known as '' Network Computer s'' or hybrid clients. ''Hybrid client'' may either just mean diskless node, or it may be used in a more particular sense to mean a diskless node which runs ''some'', but not all, Applications remotely, as in the Thin Client computing architecture. Advantages of diskless nodes can include lower production cost, lower running costs, quieter operation, and manageability advantages (for example, centrally-managed software installation). In many universities and in some large organisations, PC s are used in a similar configuration, with some or all applications stored remotely but Executed locally—again, for manageability reasons. However, these are not diskless nodes if they still Boot from a local Hard Drive . DISTINCTION BETWEEN DISKLESS NODES AND CENTRALIZED COMPUTING Diskless nodes process Data , thus using their own CPU and RAM to run Software , but do not store data persistently—that task is handed off to a server. This is distinct from Thin Client s, in which all significant processing happens remotely, on the server—the only software that runs on a thin client is the "thin" client software, which handles simple input/output tasks to communicate with the user, such as drawing a Dialog Box on the Display or waiting for user input. A collective term encompassing both thin client computing, and its technological predecessor, Text Terminal s (which are text-only), is Centralized Computing . Thin Client s and Text Terminal s can both require powerful central processing facilities in the servers, in order to perform all significant processing tasks for all of the clients. Diskless nodes can be seen as a compromise between Fat Client s (such as ordinary Personal Computer s) and centralized computing, using central storage for efficiency, but not requiring centralized processing, and making efficient use of the powerful processing power of even the slowest of contemporary CPUs , which would tend to sit idle for much of the time under the centralized computing model. BOOTSTRAP OPERATION The operating system (OS) for a diskless node is loaded from a server, using Network Booting . In some cases, removable storage may be used to initiate the bootstrap process, such as a USB Flash Drive , or other bootable media such as a Floppy Disk , CD or DVD. However, the Firmware in many modern computers can be configured to locate a server and begin the bootup process automatically, without the need for any bootable media. After the bootstrapping process has been initiated, as described above, bootstrapping will take place according to one of three main approaches.
For some versions of Windows , a simple "network booted" system can be constructed by launching MS-DOS from a locally attached floppy disk and using NetBIOS API based protocols (e.g., NBF or DECnet ) to access a network "share" containing the OS image {Link without Title} . After loading the OS, control has to be passed from the bootstrap program to the OS itself. This has for a long time been considered impossible with modern servers {Link without Title} . Third party software Vendors such as Qualystem (acquired by (Qualystem) and Citrix Ardence . COMPARISON WITH FAT CLIENTS Software installation and maintenance With essentially a single OS image for an array of machines (with perhaps some customizations for differences in Hardware configurations among the nodes), installing software and maintaining installed software can be more efficient. Furthermore, any System Change s made during operation (due to user action, worms, viruses, etc.) can be either wiped out when the power is removed (if the image is copied to a local RAM disk) or prohibited entirely (if the image is a network filesystem). This allows use in public access areas (such as Libraries ) or in schools etc. where users might wish to experiment or attempt to "hack" the system. However, it is not necessary to implement network booting to achieve either of the above advantages - ordinary PCs (with the help of appropriate software) can be configured to download and reinstall their operating systems on (e.g.) a nightly basis. Centralized storage The use of central disk storage also makes more efficient use of disk storage. This can cut storage costs, freeing up capital to Invest in more reliable, modern storage technologies, such as RAID Array s which support redundant operation, and Storage Area Network s which allow hot-adding of storage without any interruption. Further, it means that losses of disk drives to mechanical or electrical failure—which are statistically highly probable events over a timeframe of years, with a large number of disks involved—are often both less likely to happen (because there are typically less disk drives that can fail) and less likely to cause interruption (because they would likely be part of RAID arrays). This also means that the nodes ''themselves'' are less likely to have hardware failures than Fat Client s. Diskless nodes share these advantages with Thin Client s. Performance of centralized storage However, this storage efficiency can come at a price. As often happens in computing, increased storage efficiency sometimes comes at the price of decreased performance. Large numbers of nodes making demands on the same server simultaneously can slow down everyone's experience. However, this can be mitigated by installing large amounts of RAM on the server (which speeds up read operations by improving Caching performance), by adding more servers (which distributes the I/O workload), or by adding more disks to a RAID array (which distributes the ''physical'' I/O workload). In any case this is also a problem which can affect ''any'' client-server network to some extent, since, of course, fat clients also use servers to store user data. Indeed, user data may be much more significant in size and may be accessed far more frequently than operating systems and programs in some environments, so moving to a diskless model will not ''necessarily'' cause a noticeable degradation in performance. Greater Network Bandwidth (i.e. capacity) will also be used a diskless model, compared to a fat client model. This does not necessarily mean that a higher capacity network infrastructure will need to be installed—it could simply mean that a higher proportion of the existing network capacity will be used. Finally, the combination of network data transfer Latencies (physically transferring the data over the network) and contention latencies (waiting for the server to process other node's requests before yours) can lead to an unacceptable degradation in performance compared to using local drives, depending on the nature of the application and the capacity of the network infrastructure and the server. Other advantages Another example of a situation where a diskless node would be useful is in a possibly hazardous environment where computers are likely to be damaged or destroyed, thus making the need for inexpensive nodes, and minimal hardware a benefit. Again, thin clients can also be used here. Diskless machines also consume little power and make little noise, which implies potential Environmental Benefits and makes them ideal for some Computer Cluster applications. COMPARISON WITH THIN CLIENTS Major corporations tend to instead implement Thin Client s (using Microsoft Windows Terminal Server or other such software), since much lower specification hardware can be used for the client (which essentially acts as a simple "window" into the central server which is actually running the users operating system as a Login Session ). Of course, diskless nodes can also be used as thin clients. Moreover, thin client computers are increasing in power to the point where they are becoming suitable as fully-fledged diskless workstations for some applications. Both thin client and diskless node architectures employ diskless clients which have advantages over fat clients (see above), but differ with regard to the location of processing. Advantages of diskless nodes over thin clients
Advantages of thin clients over diskless nodes
REFERENCES
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