File System Types：
AIX supports multiple file system types. These include the following:
Journaled File System (JFS) or Enhanced Journaled File System (JFS2)
Network File System (NFS)
CD-ROM File System (CDRFS)
DVD-ROM File System (UDFS)
Journaled File System (JFS) or Enhanced Journaled File System (JFS2)
Supports the entire set of file system semantics. These file systems use database journaling techniques to maintain structural consistency. This prevents damage to the file system when the system is halted abnormally.
Each JFS or JFS2 resides on a separate logical volume. The operating system mounts the file system during initialization. This multiple file system configuration is useful for system management functions such as backup, restore, and repair, because it isolates a part of the file tree so that you can work on it.
A difference between JFS and JFS2 is that JFS2 is designed to support large files and large file systems. These file system types are described more thoroughly in Understanding JFS and JFS2.
Network File System (NFS)
Is a distributed file system that allows users to access files and directories located on remote computers and use those files and directories as if they were local. For example, users can use operating system commands to create, remove, read, write, and set file attributes for remote files and directories. NFS is described more thoroughly in the AIX 5L Version 5.2 Security Guide.
CD-ROM File System (CDRFS)
Allows access to the contents of a CD-ROM through the normal file system interfaces. CDRFS is described more thoroughly in Understanding CDRFS.
DVD-ROM File System (UDFS)
Allows access to the contents of a DVD through the normal file system interfaces. UDFS is described more thoroughly in Understanding UDFS.
Understanding JFS and JFS2
The journaled file system (JFS) and the enhanced journaled file system (JFS2) are built into the base operating system. Both file system types link their file and directory data to the structure used by the AIX Logical Volume Manager for storage and retrieval. A difference is that JFS2 is designed to accommodate a 64-bit kernel and larger files.
The following sections describe these file systems. Unless otherwise noted, the following sections apply equally to JFS and JFS2.
JFS2
JFS2 (enhanced journaled file system) is a file system, introduced in AIX 5L for POWER Version 5.1, that provides the capability to store much larger files than the existing Journaled File System (JFS). Customers can choose to implement either JFS, which is the recommended file system for 32-bit environments, or JFS2, which offers 64-bit functionality.
Note:
Unlike the JFS file system, the JFS2 file system will not allow the link() API to be used on files of type directory. This limitation may cause some applications that operate correctly on a JFS file system to fail on a JFS2 file system.
The following table provides a summary of JFS and JFS2 functions:
Functions JFS2 JFS
Fragments/Block Size 512-4096 Block sizes 512-4096 Frags
Maximum file system size 16 Terabytes 1 Terabyte
Maximum file size 16 Terabytes 64 GB
Number of i-nodes Dynamic, limited by disk space Fixed, set at file-system creation
Directory organization B-tree Linear
Compression No Yes
Quotas No Yes
Note:
The maximum file size and maximum file system size is limited to 1 Terabyte when used with the 32-bit kernel.
Understanding Disk Space Segmentation
Many UNIX file systems only allocate contiguous disk space in units equal in size to the logical blocks used for the logical division of files and directories. These allocation units are typically referred to as disk blocks and a single disk block is used exclusively to store the data contained within a single logical block of a file or directory.
Using a relatively large logical block size (4096 bytes for example) and maintaining disk block allocations that are equal in size to the logical block are advantageous for reducing the number of disk I/O operations that must be perf
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