The Impact of Disk Fragmentation

The Impact of
Disk Fragmentation
by Joe Kinsella
While there is little dispute among IT professionals regarding the impact of disk fragmenta-tion on system performance, no independent guidelines exist to recommend the frequencyof defragmentation across an infrastructure. Some IT professionals use defragmentation asa measure of last resort, defragmenting only after system performance has sufficientlydegraded to make its impact directly noticeable to users. Others proactively schedule diskdefragmentation regularly, with the intent of eliminating the gradual accumulation of fragmented files.While just about every IT professional has his or her fragmentation horror story - about a system on which fragmentation had so severely degraded performance that it wasunusable - very few can offer more than anecdotal evidence regarding the use and impor-tance of defragmentation software.I recently decided to put fragmentation to the test, with the intent of answering twobasic questions:1. What impact does fragmentation have on user and system activities?2. How quickly does fragmentation accumulate as a result of these activities?
This white paper will outline the results of the testing, draw conclusions, and make recommendations regarding managing fragmentation across your infrastructure.? Contents
The Mechanics of Disks ......................1 The Impact NTFS ....................................................2
The Cause of Fragmentation................3 of DiskThe Approach to Testing ......................3
The Impact of Fragmentation ..............4 FragmentationMicrosoft Word ................................4
Microsoft Outlook ............................4
Microsoft Internet Explorer ..............5
Microsoft Anti-Spyware ..................5
Grisoft AVG Anti-Virus Scanner............................................6
The Impact of Defragmentation............6 The Mechanics of DisksThe Accumulation of Fragmentation ......................................7 The basic components of hard disks (see Figure 1) have not changed significantly since their invention in the 1950s. Hard disks have one orUnderneath the Hood ..........................8 more polished platters made of aluminum or glass that hold a magneticmedium used for storing information. The platters are stacked onto a Recommended Policy ..........................8 spindle and rotated by a spindle motor at very high speeds, often in excessof 160 miles per hour. A platter has concentric circles called tracks, andConclusions ..........................................9 each track is divided into small sections called sectors, each capable ofholding a fixed amount of information.Small devices called heads are responsible for the actual reading andwriting of data on the platter. Each platter has two heads (for the top andbottom), and the heads are mounted on sliders positioned over the surfaceof the disks, which in turn are mounted on arms. The entire assembly isconnected to and controlled by an actuator, which in turn is connected to alogic board that allows for the communication between a computer andthe hard disk.To read or write information to the disk, an application makes a requestof an operating system to create, modify or delete a file. The operating sys-tem then translates the logical request into a physical request containingthe actual locations to be read or written on the hard disk. The logic boardthen instructs the actuator to move the heads to the appropriate track, andCopyright 2005 Diskeeper Corporation. All rights reserved to read or write the appropriate sectors from the rotating platter below.original image © Seagate Technology image used with permission
Cover
Head/DiscE Block AssemblyDiscs
Actuator SpindleDC Power InputRead/Write HeadsBase CastingShock MountPrintedCircuit Cable I/O ConnectorPrinted Circuit BoardFrame/Bracket
Connector
Figure 1: Overview of Hard Disk
The mechanical movement of the head across a platter file system is not a pre-requisite to understanding fragmen-is typically one of the most expensive operations of a hard tation, it will help clarify both the terminology used as welldisk. As a result, most operating systems seek to minimize as the test results.this head movement through caching, optimizing I/O NTFS was created by Microsoft in the 1990s as part of requests, and streamlining the storage of data on a disk... [download for more]