metertore.blogg.se - Volume manager

#Volume manager software
#Volume manager code
#Volume manager Offline

A RAID 1 backend device (a PV) can be configured as "write-mostly", resulting in reads being avoided to such devices unless necessary.

Entire LVs or their parts can be striped across multiple PVs, similarly to RAID 0.

LVs can be created to include RAID functionality, including RAID 1, 5 and 6.

This prevents LVM from activating volumes on an individual path instead of the multipath device.

On newer versions of device mapper, LVM is integrated with the rest of device mapper enough to ignore the individual paths that back a dm-multipath device if devices/multipath_component_detection=1 is set in lvm.conf.

Thinly provisioned LVs can be allocated from a pool.

Hybrid volumes can be created using the dm-cache target, which allows one or more fast storage devices, such as flash-based SSDs, to act as a cache for one or more slower hard disk drives.

VGs and LVs can be made active as the underlying devices become available through use of the lvmetad daemon.LVM objects can be tagged for administrative convenience.

#Volume manager Offline

This can be useful when migrating whole LVs to or from offline storage. VGs can be split or merged in situ as long as no LVs span the split.Creation of read-only snapshots of logical volumes (LVM1), leveraging a copy on write (CoW) feature, or read/write snapshots (LVM2).Logical volumes (LVs) can be resized online by concatenating extents onto them or truncating extents from them.Volume groups (VGs) can be resized online by absorbing new physical volumes (PVs) or ejecting existing ones.Various elements of the LVM Basic functionality

#Volume manager software

LVM can be considered as a thin software layer on top of the hard disks and partitions, which creates an abstraction of continuity and ease-of-use for managing hard drive replacement, repartitioning and backup. Encrypting multiple physical partitions with one password.

Performing consistent backups by taking snapshots of the logical volumes.

On small systems (like a desktop), instead of having to estimate at installation time how big a partition might need to be, LVM allows filesystems to be easily resized as needed.

Managing large hard disk farms by allowing disks to be added and replaced without downtime or service disruption, in combination with hot swapping.

Creating single logical volumes of multiple physical volumes or entire hard disks (somewhat similar to RAID 0, but more similar to JBOD), allowing for dynamic volume resizing.

#Volume manager code

Heinz Mauelshagen wrote the original LVM code in 1998, when he was working at Sistina Software, taking its primary design guidelines from the HP-UX's volume manager. Most modern Linux distributions are LVM-aware to the point of being able to have their root file systems on a logical volume. In Linux, Logical Volume Manager ( LVM) is a device mapper framework that provides logical volume management for the Linux kernel.