2 Configuring LVM
By default, the LVM commands are already installed on your system. This chapter discusses issues
to consider when setting up your logical volumes. It addresses the following topics:
•
“Planning Your LVM Configuration” (page 20)
•
“Setting Up Different Types of Logical Volumes” (page 20)
•
“Planning for Availability” (page 24)
•
“Planning for Recovery” (page 34)
•
“Planning for Performance” (page 29)
Planning Your LVM Configuration
Using logical volumes requires some planning. Some of the issues to consider for planning purposes
are discussed in this chapter. Consider these issues before setting up or modifying logical volumes
on your system.
•
For what purpose will you use a logical volume? For raw data or a file system? As a swap
area or dump area? See
“Setting Up Different Types of Logical Volumes” (page 20)
.
•
How big will you make a logical volume?
•
Does your data require high availability? If so, consider mirroring your logical volume across
multiple disks, as described in
“Increasing Data Availability Through Mirroring” (page 24)
.
Also consider setting up spare disks to handle mirror failure, as described in
“Increasing Disk
Redundancy Through Disk Sparing” (page 27)
.
•
Is I/O performance very important to you? If so, consider striping your logical volumes across
multiple disks, as described in
“Increasing Performance Through Disk Striping” (page 31)
,
and separating I/O channels, as described in
“Increasing Performance Through I/O Channel
Separation” (page 33)
. For additional recommendations for performance, read
“Planning for
Performance” (page 29)
.
•
Do you need to balance high availability and I/O performance? If so, consider striping and
mirroring your logical volume, as described in
“Increasing Data Availability Through Mirroring”
(page 24)
and
“Increasing Performance Through Disk Striping” (page 31)
.
•
Is it important to recover from disk failures quickly? If so, see
“Planning for Recovery” (page 34)
.
Setting Up Different Types of Logical Volumes
This section contains information on setting up special logical volumes.
Setting Up Logical Volumes for Raw Data Storage
You can optimize raw I/O performance by planning your logical volumes specifically for raw data
storage. To create a raw data logical volume (such as for a database), consider how large the
logical volume must be and how such a logical volume is distributed over your disks.
Typically, you specify the size of a logical volume in megabytes. However, a logical volume must
be a multiple of the extent size used in the volume group. For example, if a database partition
requires 2002 MB and the logical extent size is 4 MB, LVM creates a logical volume that is 2004
MB (or 501 logical extents).
If you plan to use logical volumes heavily for raw data storage (such as for setting up database
partitions), consider how the logical volumes are distributed over your disks.
By default, LVM assigns disk space for a logical volume from one physical volume, uses the space
on this physical volume entirely, then assigns space from each successive physical volume in the
same manner. LVM uses the physical volumes in the order in which they appear in
/etc/lvmtab
20
Configuring LVM
