Installation guide

Chapter 1.
1
The LVM Logical Volume Manager
This chapter provides a summary of the features of the LVM logical volume manager that are new for
the initial and subsequent releases of Red Hat Enterprise Linux 6. Following that, this chapter provides
a high-level overview of the components of the Logical Volume Manager (LVM).
1.1. New and Changed Features
This section lists new and changed features of the LVM logical volume manager that are included with
the initial and subsequent releases of Red Hat Enterprise Linux 6.
1.1.1. New and Changed Features for Red Hat Enterprise Linux 6.0
Red Hat Enterprise Linux 6.0 includes the following documentation and feature updates and changes.
• You can define how a mirrored logical volume behaves in the event of a device failure with
the mirror_image_fault_policy and mirror_log_fault_policy parameters in the
activation section of the lvm.conf file. When this parameter is set to remove, the system
attempts to remove the faulty device and run without it. When this parameter is set to allocate,
the system attempts to remove the faulty device and tries to allocate space on a new device to be
a replacement for the failed device; this policy acts like the remove policy if no suitable device and
space can be allocated for the replacement. For information on the LVM mirror failure policies, see
Section 4.4.3.1, “Mirrored Logical Volume Failure Policy”.
• For the Red Hat Enterprise Linux 6 release, the Linux I/O stack has been enhanced to process
vendor-provided I/O limit information. This allows storage management tools, including LVM, to
optimize data placement and access. This support can be disabled by changing the default values
of data_alignment_detection and data_alignment_offset_detection in the lvm.conf
file, although disabling this support is not recommended.
For information on data alignment in LVM as well as information on changing the default values
of data_alignment_detection and data_alignment_offset_detection, see the inline
documentation for the /etc/lvm/lvm.conf file, which is also documented in Appendix B, The
LVM Configuration Files. For general information on support for the I/O Stack and I/O limits in Red
Hat Enterprise Linux 6, see the Storage Administration Guide.
• In Red Hat Enterprise Linux 6, the Device Mapper provides direct support for udev integration.
This synchronizes the Device Mapper with all udev processing related to Device Mapper devices,
including LVM devices. For information on Device Mapper support for the udev device manager,
see Section A.3, “Device Mapper Support for the udev Device Manager”.
• For the Red Hat Enterprise Linux 6 release, you can use the lvconvert --repair command to
repair a mirror after disk failure. This brings the mirror back into a consistent state. For information
on the lvconvert --repair command, see Section 4.4.3.3, “Repairing a Mirrored Logical
Device”.
• As of the Red Hat Enterprise Linux 6 release, you can use the --merge option of the lvconvert
command to merge a snapshot into its origin volume. For information on merging snapshots, see
Section 4.4.5, “Merging Snapshot Volumes”.
• As of the Red Hat Enterprise Linux 6 release, you can use the --splitmirrors argument of the
lvconvert command to split off a redundant image of a mirrored logical volume to form a new
logical volume. For information on using this option, see Section 4.4.3.2, “Splitting Off a Redundant
Image of a Mirrored Logical Volume”.