AIX > Administrator > Systems Management

Storage Management in AIX 5L Version 5.3

Updates to the Logical Volume Manager (LVM).

Note: This article can also be found on the IBM Developerworks Web site.

When this article was first published in April 2005 under the title Logical Volume Manager in AIX 5L Version 5.3, it discussed a number of features that were introduced in AIX 5L* Version 5.3 to enhance the scope, functionality, and performance of the Logical Volume Manager (LVM). The next major enhancements to AIX 5L were introduced in the 5300-03 maintenance level, which was released in September 2005. This article is an updated and expanded version of the April 2005 publication. While the original content has been retained almost in its entirety, the article has been augmented by including a discussion of some of the LVM enhancements introduced in the 5300-03 maintenance level. Also, its scope has been broadened to cover a number of improvements, introduced both in the original release of the AIX 5L Version 5.3 and the 5300-03 maintenance level, to the Enhanced Journal File System (JFS2). In the following discussions, I use the expression (5300-03) to indicate that the referenced feature is available only for the 5300-03 maintenance level and beyond.

LVM command enhancements

In AIX 5L Version 5.3, changes have been made to the following LVM commands to enhance their performance, such as they require less execution time than their counterparts in prior releases of AIX*:

• extendvg
• importvg
• mkvg
• varyonvg
• chlvcopy
• mklvcopy
• lslv
• lspv

Concurrent mode (classical and enhanced)

The classical concurrent mode volume groups (VGs) only supported Serial DASD and SSA disks in conjunction with the 32-bit kernel. AIX 5L Version 5.1 overcame the restriction of supported disk types by introducing the so-called enhanced concurrent mode VG, which extended the concurrent mode support to all other disk types. While AIX 5L Version 5.2 did not allow creation of classical concurrent mode VGs, it did support them. The support for classical concurrent mode VGs has been completely removed from AIX 5L Version 5.3. When trying to import a classical concurrent mode VG in AIX 5L Version 5.3, an error message informs the user to convert the VG to enhanced concurrent mode.

VGs (normal, big, and scalable)

The VG type, commonly known as standard or normal, allows a maximum of 32 physical volumes (PVs). A standard or normal VG is no more than 1016 physical partitions (PPs) per PV and has an upper limit of 256 logical volumes (LVs) per VG. Subsequently, a new VG type was introduced which was referred to as big VG. A big VG allows up to 128 PVs and a maximum of 512 LVs.

AIX 5L Version 5.3 has introduced a new VG type called scalable volume group (scalable VG). A scalable VG allows a maximum of 1024 PVs and 4096 LVs. The maximum number of PPs applies to the entire VG and is no longer defined on a per disk basis. This opens up the prospect of configuring VGs with a relatively small number of disks and fine-grained storage allocation options through a large number of PPs, which are small in size. The scalable VG can hold up to 2,097,152 (2048 K) PPs. As with the older VG types, the size is specified in units of megabytes and the size variable must be equal to a power of 2. The range of PP sizes starts at 1 (1 MB) and goes up to 131,072 (128 GB). This is more than two orders of magnitude above the 1024 (1 GB), which is the maximum for both normal and big VG types in AIX 5L Version 5.2. The new maximum PP size provides an architectural support for 256 petabyte disks. Table 1 below shows the variation of configuration limits with different VG types. Note that the maximum number of user definable LVs is given by the maximum number of LVs per VG minus 1 because one LV is reserved for system use. Consequently, system administrators can configure 255 LVs in normal VGs, 511 in big VGs, and 4095 in scalable VGs.

The scalable VG implementation in AIX 5L Version 5.3 provides configuration flexibility with respect to the number of PVs and LVs that can be accommodated by a given instance of the new VG type. The configuration options allow any scalable VG to contain 32, 64, 128, 256, 512, 768, or 1024 disks and 256, 512, 1024, 2048, or 4096 LVs. You do not need to configure the maximum values of 1024 PVs and 4096 LVs at the time of VG creation to account for potential future growth. You can always increase the initial settings at a later date as required.

Tweet