![]() These fragments are set aside for the i-nodes at file system creation and extension time. The first 4096 bytes of this area hold the boot block and the second 4096 bytes hold the file system superblock.Įach allocation group contains a static number of contiguous disk i-nodes which occupy some of the group's fragments. The first of these groups begins the file system and contains a reserved area occupying the first 32 x 4096 bytes of the group. The set of fragments making up the file system are divided into one or more fixed-sized units of contiguous fragments. Instead, the i-node points to an indirect block which contains the additional addresses. If a file has a large number of logical blocks, the i-node does not contain the disk addresses. ![]() One address contains the first 4096 bytes and a second address contains the remaining 2048 bytes (a partial logical block). A larger file with a size of 6144 bytes has two addresses. Its 4096 bytes of data are contained in a single logical block. For example, a file with a size of 4096 bytes has a single address on the i-node's array. These addresses indicate the starting fragment and the total number of fragments included in a single allocation. Each section contains an address for one of the file or directory's logical blocks. These i-nodes also contain "addresses" for finding the location on the disk where the data for a logical block is stored.Įach i-node has an array of numbered sections. Each file and directory has an i-node that contains access information such as file type, access permissions, owner's ID, and number of links to that file. Each logical block is allocated fragments for the storage of its data. Disk I-NodesĪ logical block contains a file or directory's data in units of 4096 bytes. ![]() "File Space Allocation" explains how the operating system allocates fragments. In addition to containing data for files and directories, fragments also contain disk addresses and data for indirect blocks. The default JFS fragment size is 4096 bytes, although you can specify smaller sizes. Thus, fragment allocations can span the boundaries of what might otherwise be a disk block. JFS fragments are the basic allocation unit and the disk is addressed at the fragment level. The journaled file system (JFS), however, provides a view of the file system as a contiguous series of fragments. In other words, a logical block cannot be allocated fragments from different disk blocks. Some systems do not allow fragment allocations to span the boundaries of the disk block. The disk block may be further divided into fixed-size allocation units called fragments. These blocks divide the disk into units of equal size to store the data in a file or directory's logical blocks. Many file systems have disk blocks or data blocks. The disk i-node allocation map records the status of each i-node.The fragment allocation map records the allocation state of each fragment.The file system contains two allocation bitmaps: A flag indicating the state of the file system.Number of data blocks in the file system.The super- block maintains information about the entire file system and includes the following fields: The superblock is 4096 bytes in size and starts at byte offset 4096 on the disk. ![]() The boot block is available to start the operating system. The boot block occupies the first 4096 bytes of the file system starting at byte offset 0 on the disk. Each file system occupies one logical volume. An allocation group contains disk i-nodes and fragments. In addition to files and directories, file systems contain a boot block, a superblock, bitmaps, and one or more allocation groups. File systems maintain information and identify where a file or directory's data is located on the disk. AIX Version 4.3 General Programming Concepts: Writing and Debugging ProgramsĪ file system is a set of files, directories, and other structures. ![]()
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