Disk and File system overview for AIX

1. System Catalogue

2. Logical Volume Management

Before you know how AIX handles file systems, it's a good idea to have a basic understanding of LVM (logical volume management) first. LVM is a disk management approach that is completely different from traditional UNIX partitioning policies. One of its advantages is that it allows you to dynamically allocate more space to a file system. The components of LVM are physical volumes (PV), volume groups (VG), physical partitions (PP), logical volumes (LV), and logical partitions (LP).

3. Basic concepts:

Physical Volume: A physical volume refers to a hard disk.

Volume Group: A volume group is a collection of available physical hard disks that can be logically viewed as a large hard drive. A volume group consists of one or more physical volumes, up to 32 (the value has increased to 128 under the AIX4.3.2 version).

Physical partitions: The physical volumes in a volume group are divided into fixed-size blocks (the default is 4MB), and such blocks are called physical partitions.

Logical volumes: one or more logical volumes can be defined in each volume group, which is a collection of information located on a physical partition (can be a file system, paging space, log or dump device space, and so on).

Allows you to create logical volumes in a mirrored manner.

When you create a logical volume, you can specify that the data be allocated in a compartmentalized manner (as described in the first chapter). "Compartmentalization" distributes data blocks evenly across multiple disks to improve read-write performance.

Logical partitions: Logical volumes consist of a number of logical partitions.

Because the default size of the logical partition (corresponding to the corresponding physical partition) is 4MB, the logical volume with 64 logical partitions is assigned a size of 256MB.

Without mirroring, physical partitions and logical partitions are one-to-one relationships that can be mirrored by assigning two or three physical partitions to a logical partition.

Logical partitions in logical volumes are arranged sequentially for the user, but the corresponding physical partitions can be distributed, unordered, from different locations on the disk or from different disks.

Log file System: A logical volume can contain paging and dump space, but is usually used as a file system.

The structure of the AIX file system is very similar to that of other UNIX systems. As a log file system (JFS), each AIX file system contains super blocks, I nodes, and data blocks.

The log file system replaces fsck with logs and is used to recover the file system in the case of a failure.

A JFS is not confined to an entire disk as a layered file system (HFS) in other Unix, nor is it required to be distributed on contiguous disk space.

JFS writes data in blocks of 4 K and also supports BSD-style fragmentation dimensions (minimum 512 bytes) to increase disk utilization.

JFS also supports the LZ algorithm for file compression and decompression.