IBM Journaled File System 2 (JFS2)
| Developer(s) | IBM et al. |
|---|---|
| Full name | IBM Journaled File System |
| Introduced | 1990 and 1999 with JFS1 in AIX 3.1 and JFS in OS/2 4.5 |
| Partition identifier | 0x35 (MBR) |
| Structures | |
| Directory contents | B+ tree |
| File allocation | Bitmap/extents |
| Limits | |
| Max. volume size | 32 PB (32 × 10245 bytes) |
| Max. file size | 4 PB (4 × 10245 bytes) |
| Max. number of files | No limit defined |
| Max. filename length | 255 bytes |
| Allowed characters in filenames | Any Unicode except NUL |
| Features | |
| Dates recorded | Modification (mtime), Attribute modification (ctime), Access (atime) |
| Date resolution | 1ns |
| Forks | Yes |
| Attributes | Yes |
| File system permissions | POSIX, ACLs |
| Transparent compression | Only in JFS1 on AIX |
| Transparent encryption | No (provided at the block device level) |
| Data deduplication | No |
| Other | |
| Supported operating systems | AIX, OS/2, Linux |
Journaled File System or JFS is a 64-bit journaling file system created by IBM. There are versions for AIX, eComStation, OS/2, and Linux operating systems. The latter is available as free software under the terms of the GNU General Public License (GPL). HP-UX has another, different filesystem named JFS that is actually an OEM version of Veritas Software's VxFS.
In the AIX operating system, there exist two generations of JFS filesystem that are called JFS (JFS1) and JFS2 respectively. In the other operating systems, such as OS/2 and Linux, only the second generation exists and is called simply JFS. This should not be confused with JFS in AIX that actually refers to JFS1.
IBM introduced JFS with the initial release of AIX version 3.1 in February, 1990. This file system, now called JFS1 on AIX, had been the premier file system for AIX over the following decade and had been installed in thousands or millions of customers' AIX systems. Historically, the JFS1 file system is very closely tied to the memory manager of AIX, which is a typical design for a file system supporting only one operating system. JFS was one of the first file systems to support Journaling
In 1995, work began to enhance the file system to be more scalable and to support machines that had more than one processor. Another goal was to have a more portable file system, capable of running on multiple operating systems. After several years of designing, coding, and testing, the new JFS was first shipped in OS/2 Warp Server for eBusiness in April, 1999, and then in OS/2 Warp Client in October, 2000. In December, 1999, a snapshot of the original OS/2 JFS source was granted to the open source community and work was begun to port JFS to the Linux operating system. The first stable release of JFS for Linux appeared in June, 2001. The JFS for Linux project is maintained by a small group of contributors known as the JFS Core Team. This release of sources also worked to form the basis of a re-port back to OS/2 of the open-source JFS.
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