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Large files (large). If the data file is placed in one account MET, that fact is reflected in the title attribute Data, which contains a sign that this attribute is a resident, which is located in segments outside tables MFT. In this case, Data attribute contains the address information (LCN, VCN, k) each segment data (Figure 7.21). Fig. 7.22. Huge file Extreme files (extremely huge). For extreme file attribute Attribute List can specify multiple attributes of the additional entries MFT (Figure 7.23). You can also use a double indirect addressing, when nerezidentny attribute will link to other non-resident attributes, so NTFS attributes may not be too much for the length. Very large files (huge). If the file is so great that its attribute data store addresses resident segments data is not stored in one record, this attribute is placed in another account MFT, a reference to attribute this to the main entry file (Figure 7.22). This link is contained in the attribute Attribute List. Sam attribute data continues to address resident data segments. Catalogs NTFS Each directory NTFS is one entrance to the MFT table, which contains an attribute Index Root. The index contains a list of files in the directory. Indices can sort files to speed up the search based on the value of certain attributes. Usually, file systems, files sorted by name. NTFS allows for sorting any attribute, if it is stored in a resident. There are two forms of storing the list of files. Small directories (small indexes). If the number of files in the directory is not a list of the files can be resident in writing MFT, a directory (see Figure 7.24). For a list of resident storage is the only attribute-Index Root. File contains a list of file attributes. By default, the filename, as well as the record number MTF, a record primary file. Large catalogues (large indexes). As the directory grows, the list of files may require resident of storage. However, the initial list is always resident in the root directory entry in the table MFT (Figure 7.25). Filenames resident of the list of files are called nodes Finally tree (binary tree). The rest of the list of files located outside MFT. Their search is a special attribute Allocation Index, representing addresses segments, the remaining holders of the list folder. Some of the lists are the leaves of a tree, while others are intermediate nodes, which is contained along with the names of files attribute Index Allocation indicating lists of files at lower levels. Sites binary tree divided the entire list of files into several groups. Debug output log file name of each node is the name of the last file in the group. It is believed that the file names compared leksikograficheski, it is first taken into account codes first two characters compared names, the name is less if the code of the first character is less arithmetic value, equality code first characters compares codes second character names and e. For example, the file f 1. ehe, the first node of the binary tree shown in Fig. 7.25 is the name leksikograficheski big names avia.exe, az.exe ,..., emax.exe forming the first list of names directory. Accordingly file ltr.exe has addressed most of the second group of names, and all files with the names, big ltr.exe, a third and final group. Search Directory unique filename, which is NTFS number of major record in the MFT file, it is a symbolic name to read. First, a symbolic name searches compared to the first node in the name of the resident part of the index. If fewer original name, it means that it has to be sought in the first resident group, which of the attributes Index Allocation pulled to the segment (VCNj, LCN ^ K!) , Keeps files first. Among the names of the group is done directly display the names and compared to a convergence of characters from the original name stored in the directory name. If convergence is extracted from the catalogue number of major record file in MFT and other characteristics of the file are there. If the original name more name first node resident of the index, then compare it with the name of the second node, and if the original name below, the described procedure is the second resident group names, etc. As a result, instead perebora many names (in the worst case, all the name directory) is compared with a much smaller number of nodes and names names in a group directory. If one group becomes too large directory, it is also divided into groups, each of the last names of the new team left in the original nerezidentnom attribute Index Root, and all the other names on new teams moving into new non-resident type attributes Index Root (in the figure did not show ). By starting nerezidentnomu attribute Index Root added attribute of the index, indicating sections index of new groups. If you now to find the desired name in the resident part of the index level a comparison shows that the original name is less than one name kept there, it is said that this attribute accurate comparison is to be named could not be turning to the sub names next level tree. File operations Two ways of file operations File System OS should allow users operations set of files, designed in the form of system calls. This usually consists of a set of system calls, as creat (a file), read (read from a file), write (write to a file) and some others. Most of the same file the user is not one operation, a sequence of operations. For example, when a text editor, file, which contains a document, the user typically reads a few pages of text, editing the data and write them on a matter and then reads a page from another file, etc. After many operations reading and writing user completes work with the file and moves to another. Whatever operations are not performed on the file, the OS must perform certain universal for all operations of action: 1. On the symbolic name of the file found its properties, which are stored in the file system on the disk. 2. Copy features file into RAM, as the only way code can be used. 3. Based on the characteristics of the file to verify the user to perform the requested operation (read, write, delete, view file attributes). 4. Clear the area of memory reserved under the temporary storage of files. In addition, each transaction includes some unique for its action, such as reading a set of clusters disk file management, etc. The operating system can perform the steps of the file in two ways (Figure 7.26): For each operation performed as universal or unique action. This is sometimes called the scheme without memory of Operations (stateless). All of universal performed at the beginning and end of the sequence of operations, and for each sub-operations are performed only unique action. The vast majority of file systems supported a second method of file operations as a more economical and faster. The first method has one advantage-it is more resistant to breakdown in the system, because every operation is self-sufficient and not dependent on the previous result. Therefore, the first method is sometimes used in distributed network file system (for example, Network File System, Sun NFS), which disrupted because of the loss of packets or failure of a network nodes more likely than local access to the files.
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