Editing Diskless node (section)

==Comparison with rich 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) such as Windows XP Embedded remote boot<ref name="microsoft5">{{cite web|url=http://msdn.microsoft.com/en-us/library/ms838569.aspx|title=Deploying Windows XP Embedded Remote Boot|first=Mark|last=Chamberlain|date=February 2004|website=[[Microsoft Developer Network]]|archive-url=https://web.archive.org/web/20120515201115/http://msdn.microsoft.com/en-us/library/ms838569.aspx|archive-date=2012-05-15}}</ref><ref name="microsoft6">{{cite web|url=http://msdn.microsoft.com/en-us/library/ms838543.aspx|title=RAM Boot Using SDI in Windows XP Embedded with Service Pack 1|first=Saad|last=Syed|date=November 2002|website=[[Microsoft Developer Network]]|archive-url=https://web.archive.org/web/20121013174724/http://msdn.microsoft.com/en-us/library/ms838543.aspx|archive-date=2012-10-13}}</ref> 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 [[personal computer|PCs]] (with the help of appropriate software) can be configured to download and reinstall their operating systems on (e.g.) a nightly basis, with extra work compared to using shared disk image that diskless nodes boot off.

Modern diskless nodes can share the very same disk image, using a 1:N relationship (1 disk image used simultaneously by N diskless nodes). This makes it very easy to install and maintain software applications: The administrator needs to install or maintain the application only once, and the clients can get the new application as soon as they boot off the updated image. Disk image sharing is made possible because they use the write cache: No client competes for any writing in a shared disk image, because each client writes to its own cache.

All the modern diskless nodes systems can also use a 1:1 Client-to-DiskImage relationship, where one client "owns" one disk image and writes directly into said disk image. No write cache is used then.

Making a modification in a shared disk image is usually made this way:

#The administrator makes a copy of the shared disk image that he/she wants to update (this can be done easily because the disk image file is opened only for reading)
#The administrator boots a diskless node in 1:1 mode (unshared mode) from the copy of the disk image he/she just made
#The administrator makes any modification to the disk image (for instance install a new software application, apply patches or hotfixes)
#The administrator shutdowns the diskless node that was using the disk image in 1:1 mode
#The administrator shares the modified disk image
#The diskless nodes use the shared disk image (1:N) as soon as they are rebooted.

===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 [[investment|invest]] in more reliable, modern storage technologies, such as [[RAID|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 fewer 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 [[rich 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 [[random-access memory|RAM]] on the server (which speeds up read operations by improving [[Cache (computing)|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, rich 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 in a diskless model, compared to a rich 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 [[latency (engineering)|latencies]] (physically transferring the data over the network) and contention latencies (waiting for the server to process other nodes' 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 may also consume little power and make little noise, which implies potential [[Environmentally friendly|environmental benefits]] and makes them ideal for some [[computer cluster]] applications.