Frag

1. Frag https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

2. IPv6 packet Fragment • In order to send a packet that is larger than the path MTU, the sending node splits the packet into fragments. The Fragment extension header carries the information necessary to reassemble the original (unfragmented) packet. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

3. IPv6 packet Fragment • Offset, in 8-octet units, relative to the start of the fragmentable part of the original packet. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

4. IPv6 packet Fragment • Packet identification value, generated by the source node. Needed for reassembly of the original packet. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

5. IPv6 packet Fragmenting • A packet containing a fragment of an original (larger) packet consists of two parts: the unfragmentable part of the original packet (which is the same for all fragments), and a piece of the fragmentable part of the original packet, identified by a fragment offset. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

6. IPv6 packet Fragmenting • The unfragmentable part of a packet consists of the fixed header and some of the extension headers of the original packet (if present): all extension headers up to and including the Routing extension header, or else the Hop-by-Hop extension header. If neither extension headers are present, the unfragmentable part is just the fixed header. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

7. IPv6 packet Fragmenting • The Next Header value of the last (extension) header of the unfragmentable part is set to 44 to indicate that a Fragment extension header follows. After the Fragment extension header a fragment of the rest of the original packet follows. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

8. IPv6 packet Fragmenting • The first fragment(s) hold the rest of the extension headers (if present). After that the rest of the payload follows. Each fragment is a multiple of 8 octets in length, except the last fragment. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

9. Defragmentation • Some defragmentation utilities try to keep smaller files within a single directory together, as they are often accessed in sequence. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

10. Defragmentation • Defragmentation is advantageous and relevant to file systems on electromechanical disk drives. The movement of the hard drive's read/write heads over different areas of the disk when accessing fragmented files is slower, compared to accessing the entire contents of a non-fragmented file sequentially without moving the read/write heads to seek other fragments. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

11. Defragmentation Causes of fragmentation • Defragmentation attempts to alleviate these problems. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

12. Defragmentation Example • An otherwise blank disk has five files, A through E, each using 10 blocks of space (for this section, a block is an allocation unit of the filesystem; the block size is set when the disk is formatted and can be any size supported by the filesystem) https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

13. Defragmentation Example • Move the file F to where it can be created as one contiguous file of the new, larger size. This would not be possible if the file is larger than the largest contiguous space available. The file could also be so large that the operation would take an undesirably long period of time. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

14. Defragmentation Example • Add a new block somewhere else, and indicate that F has a second extent (see example 5 in the image). Repeat this hundreds of times and the filesystem will have a number of small free segments scattered in many places, and some files will have multiple extents. When a file has many extents like this, access time for that file may become excessively long because of all the random seeking the disk will have to do when reading it. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

15. Defragmentation Example • In Windows, a good defragmenter will read the Prefetch files to identify as many of these file groups as possible and place the files within them in access sequence https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

16. Defragmentation Example • The reorganization involved in defragmentation does not change logical location of the files (defined as their location within the directory structure). https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

17. Defragmentation Common countermeasures • For partitions with relatively little write activity, defragmentation time greatly improves after the first defragmentation, since the defragmenter will need to defragment only a small number of new files in the future. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

18. Defragmentation Offline defragmentation • The presence of immovable system files, especially a swap file, can impede defragmentation. These files can be safely moved when the operating system is not in use. For example, ntfsresize moves these files to resize an NTFS partition. The tool PageDefrag could defragment Windows system files such as the swap file and the files that store the Windows registry by running at boot time before the GUI is loaded. Since Windows Vista, the feature is not fully supported and has not been updated. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

19. Defragmentation Offline defragmentation • Even with the improvements, the first four clusters of the MFT remain unmovable by the Windows defragmentation API, resulting in the fact that some defragmenters will store the MFT in two fragments: The first four clusters wherever they were placed when the disk was formatted, and then the rest of the MFT at the beginning of the disk (or wherever the defragmenter's strategy deems to be the best place). https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

20. Defragmentation User and performance issues • Defragmentation is just that: ensuring that there is at most one seek per file, counting only the seeks to non-adjacent tracks. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

21. Defragmentation User and performance issues • When reading data from a conventional electromechanical hard disk drive, the disk controller must first position the head, relatively slowly, to the track where a given fragment resides, and then wait while the disk platter rotates until the fragment reaches the head. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

22. Defragmentation User and performance issues • Since disks based on flash memory have no moving parts, random access of a fragment does not suffer this delay, making defragmentation to optimize access speed unnecessary. Furthermore, since flash memory can be written to only a limited number of times before it fails, defragmentation is actually detrimental (except in the mitigation of catastrophic failure). https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

23. Defragmentation Windows System Restore points may be deleted during defragmenting/optimizing • Running most defragmenters and optimizers can cause the Microsoft Shadow Copy service to delete some of the oldest restore points, even if the defragmenters/optimizers are built on Windows API. This is due to Shadow Copy keeping track of some movements of big files performed by the defragmenters/optimizers; when the total disk space used by shadow copies would exceed a specified threshold, older restore points are deleted until the limit is not exceeded. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

24. Defragmentation Defragmenting and optimizing • Besides defragmenting program files, the defragmenting tool can also reduce the time it takes to load programs and open files. For example, the Windows 9x defragmenter included the Intel Application Launch Accelerator which optimized programs on the disk. The outer tracks of a hard disk have a higher transfer rate than the inner tracks, therefore placing files on the outer tracks increases performance. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

25. Defragmentation Approach and defragmenters by file-system type • FAT: MS-DOS 6.x and Windows 9x-systems come with a defragmentation utility called Defrag. The DOS version is a limited version of Norton SpeedDisk. The version that came with Windows 9x was licensed from Symantec Corporation, and the version that came with Windows 2000 and XP is licensed from Condusiv Technologies. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

26. Defragmentation Approach and defragmenters by file-system type • There are also number of free and commercial third-party defragmentation products are available for Microsoft Windows. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

27. Defragmentation Approach and defragmenters by file-system type • BSD UFS and particularly FreeBSD uses an internal reallocator that seeks to reduce fragmentation right in the moment when the information is written to disk. This effectively controls system degradation after extended use. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

28. Defragmentation Approach and defragmenters by file-system type • In practice there are no stable and well-integrated defragmentation solutions for Linux, and thus no defragmentation is performed. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

29. Defragmentation Approach and defragmenters by file-system type • VxFS has the fsadm utility that includes defrag operations. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

30. Defragmentation Approach and defragmenters by file-system type • JFS has the defragfs utility on IBM operating systems. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

31. Defragmentation Approach and defragmenters by file-system type • HFS Plus (Mac OS X) introduced in 1998 a number of optimizations to the allocation algorithms in an attempt to defragment files while they are being accessed without a separate defragmenter. If the filesystem becomes fragmented, the only way to defragment it is to use a utility such as Coriolis System's iDefrag, or to wipe the hard drive completely and install the system from scratch. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

32. Defragmentation Approach and defragmenters by file-system type • XFS provides an online defragmentation utility called xfs_fsr. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

33. Defragmentation Approach and defragmenters by file-system type • SFS processes the defragmentation feature in almost completely stateless way (apart from the location it is working on), so defragmentation can be stopped and started instantly. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

34. Defragmentation Approach and defragmenters by file-system type • ADFS, the file system used by RISC OS and earlier Acorn Computers, keeps file fragmentation under control without requiring manual defragmentation. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

35. Defragmentation Sources • Norton, Peter (1994) Peter Norton's Complete Guide to DOS 6.22, page 521 – Sams (ISBN 067230614X) https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

36. Defragmentation Sources • Woody Leonhard, Justin Leonhard (2005) Windows XP Timesaving Techniques For Dummies, Second Edition page 456 – For Dummies (ISBN 0-764578-839). https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

37. Defragmentation Sources • Jensen, Craig (1994). Fragmentation: The Condition, the Cause, the Cure. Executive Software International (ISBN 0-9640049-0-9). https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

38. Defragmentation Sources • Dave Kleiman, Laura Hunter, Mahesh Satyanarayana, Kimon Andreou, Nancy G Altholz, Lawrence Abrams, Darren Windham, Tony Bradley and Brian Barber (2006) Winternals: Defragmentation, Recovery, and Administration Field Guide – Syngress (ISBN 1-597490-792) https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

39. Defragmentation Sources • Robb, Drew (2003) Server Disk Management in a Windows Environment Chapter 7 – AUERBACH (ISBN 0849324327) https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

40. IPv4 Fragmentation • When a router receives a packet, it examines the destination address and determines the outgoing interface to use and that interface's MTU. If the packet size is bigger than the MTU, and the Do not Fragment (DF) bit in the packet's header set to 0; the router may fragment the packet. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

41. IPv4 Fragmentation • The router divides the packet into segments. The max size of each segment is the MTU minus the IP header size (20 bytes minimum; 60 bytes maximum). The router puts each segment into its own packet, each fragment packet having following changes: https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

42. IPv4 Fragmentation • The fragment offset field is set, based on the offset of the segment in the original data payload. This is measured in units of eight-byte blocks. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

43. IPv4 Fragmentation • The header checksum field is recomputed. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

44. IPv4 Fragmentation • For example, for an MTU of 1,500 bytes and a header size of 20 bytes, the fragment offsets would be multiples of (1500–20)/8 = 185. These multiples are 0, 185, 370, 555, 740, ... https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

45. IPv4 Fragmentation • It is possible for a packet to be fragmented at one router, and for the fragments to be fragmented at another router. For example, consider a packet with a data size of 4,500 bytes, no options, and a header size of 20 bytes. So the packet size is 4,520 bytes. Assume that the packet travels over a link with an MTU of 2,500 bytes. Then it will become two fragments: https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

46. IPv4 Fragmentation • Assume that these fragments reach a link with an MTU of 1,500 bytes. Each fragment will become two fragments: https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

47. IPv4 Fragmentation • We can use the last offset and last data size to calculate the total data size: 495*8 + 540 = 3960 + 540 = 4500. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

48. IPv6 packet - Fragmentation • Unlike in IPv4, IPv6 routers never fragment IPv6 packets. Packets exceeding the size of the maximum transmission unit of the destination link are dropped and this condition is signaled by a Packet too Big ICMPv6 type 2 message to the originating node, similarly to the IPv4 method when the Don't Fragment bit is set. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

49. IPv6 packet - Fragmentation • Any data link layer conveying IPv6 data must be capable of delivering an IP packet containing 1280 bytes without the need to invoke end-to-end fragmentation at the IP layer. https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

50. IPv4 - Fragmentation and reassembly • When one network wants to transmit datagrams to a network with a smaller MTU, it may fragment its datagrams https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html