Editing Diskless node (section)

===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.