Small Sheet-fed scanners are available for as little as $200. Sheet-fed scanners are ideal for the business cards, handwritten notes, letters, and Photographs. Sheet-fed scanner allows scanning, faxing, and copying. There are many ways in which the documents can be feed into the scanner, By resting the sheet-fed scanner on its sides of the main body you can feed the document from different positions: when resting on the base plate it allows a horizontal feed-in and feed-out of the document; when on the first inclined side the inclined is in such a way that it allows a top feed-in and bottom feed-out; and when resting on the second inclined side, that allows an inclined bottom feed-in and top feed-out. Most inexpensive sheet-fed scanners are designed for black-and-white work, although newer models can handle color. You can find sheet-fed scanners that plug into your computer’s port. Disadvantages of sheet-fed scanners are that they generally can’t produce the image quality that flatbeds. Mainly because they’re trying to hit a moving target: a sheet of paper traveling over rollers. Unfortunately, not every document will feed through a sheet-fed scanner, and each sheet has to be fed one at a time. Feeding page after page into sheet-fed scanners can become quite tedious.
More specifically, it is the creation of one or more virtual instances of a “guest” operating system on top of a “host” operating system, or in some cases directly on top of a specialized software layer. It allows numerous virtual machines, either standard PCs or servers, to operate and appear as independent machines when in fact they’re operating off of a single hardware platform.
Many software providers from large to small are in the race to offer virtualization solutions, and many enterprises are taking advantage. While this futuristic technology certainly offers many benefits, it has one critical challenge to its overall performance–disk file fragmentation.
File fragmentation–the splitting of files into pieces (fragments) in order to better utilize disk space–is a performance challenge in non-virtual environments, and has been for many years. But virtualization brings with it even more critical fragmentation issues, requiring solutions like never before.
The key to understanding fragmentation’s impact on virtualization lies within the word “virtual” itself. For storage, virtual machines are making use of hard drive partitions which appear as entire drives dedicated to the virtual machines. But underneath the “virtual” layer, the hardware is storing files the way it always has, utilizing an entire disk and fragmenting files from all partitions across the whole disk.
Virtual machines have their own I/O requests which are passed along to the host system. Hence, multiple I/O requests are occurring for each file request–minimally, one request for the guest system, then another for the host system. But in a common fragmentation scenario, especially with virtual servers creating high amounts of disk activity, files will be fragmented in to tens, hundreds or even thousands of fragments. Imagine the frantic activity with multiple I/Os for each fragment of each and every file requested. The impact on performance is horrendous.
With virtualization, regular defragmentation is vital–but so is the fragmentation technology utilized. Basic defragmentation, even scheduled defragmentation, cannot possibly keep up with the fragmentation rates of virtualization. The best possible solution, one which is only now becoming available, is a constant background defragmentation solution which has no impact on system resources.