JFS in Linux Server Operating System Log Files

Article Title: JFS System in the Linux server operating system log file. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.

Developed by IBM, JFS was initially built on the AIX operating system and provides a log-based, byte-level, transaction-oriented, high-performance file system. It is scalable and robust. Compared with non-log file systems, it has the advantage of its fast restart capability: JFS can restore the file system to a consistent state in seconds or minutes. JFS is a fully 64-bit file system. All structured fields in the JFS file system are 64-bit. This allows JFS to support both large files and large partitions.
To support dce dfs (Distributed File System in a distributed computing environment), JFS combines the concept of a disk space allocation pool (called aggregation) with the installable File System subtree (called a file set) concepts are separated. Each partition has only one aggregation. Each aggregation may have multiple file sets. In the first release, JFS only supports one collection of files. However, all metadata has been designed to apply to all situations.
The starting part of the clustering is the 32 K reserved area, followed by the clustering main super block. A super block contains clustering information, such as clustering size, allocation group size, and clustering block size. Super blocks are located at a fixed position, so that JFS can find them without any other information. An important structure in clustering is the aggregation index node Table and the aggregation index node Allocation ing Table for its ing ). Inode 0 in the AIT table is retained, inode 1 describes clustering itself, inode 2 describes clustering block map (block map), and inode 3 describes embedded logs during installation, inode 4 describes the Bad blocks found during aggregation formatting and retains inode 5 to 15 for future extension. From inode 16, each inode represents a file set. The file set also has an index node table and an index node allocation ing table for its ing. inode in the file set describes every file in the file set.

JFS disk structure
JFS uses a disk-based addressing structure, along with an active block allocation policy, to generate a compact, efficient, and scalable structure that maps logical offsets in files to physical addresses on disks. A disk is a sequence of connected blocks allocated to a file as a unit. <逻辑偏移量，长度，物理地址> The productkey, devicename, and devicesecret. The addressing structure is a B + tree, which is filled by the disk Descriptor (the triples mentioned above) and is rooted in inode. The key is the logical offset of the file.
JFS dynamically allocates space for the disk inode as needed, and releases the space that is no longer needed. This feature avoids the traditional method of retaining a fixed amount of space for disk inode during file system creation. Therefore, you no longer need to estimate the maximum number of files and directories contained in the file system. In addition, this feature isolates the disk inode from the Fixed Disk location.
JFS provides two different directory organizations. The first type of organization is used for small directories and the directory content is stored in the inode of the directory. This eliminates the need for different directory blocks I/O and the need to allocate different storage. Up to 8 items can be directly stored in inode, and these items do not include themselves (.) and parent (..) directory items, which are stored in different regions of inode. The second type of organization is used for large directories. Each directory is represented by B + tree key by name. Compared with traditional unordered directory organizations, it provides faster Directory Search, insertion, and deletion capabilities.