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man: document allocation process in lvm.8
This commit is contained in:
Alasdair G Kergon
parent
6e55201144
commit
016997acaf
@ -1,5 +1,6 @@
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Version 2.02.97 -
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===============================
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Improve documention of allocation policies in lvm.8.
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Increase limit for major:minor to 4095:1048575 when using -My option.
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Add make install_systemd_generators.
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Add generator for lvm2 activation systemd units.
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190
man/lvm.8.in
190
man/lvm.8.in
@ -50,96 +50,99 @@ loading \fBlvm.conf\fP(5) and any other configuration files.
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.TP
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\fBpvdata\fP \(em Not implemented in LVM2.
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.TP
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\fBsegtypes\fP \(em Display recognised logical volume segment types.
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\fBsegtypes\fP \(em Display recognised Logical Volume segment types.
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.TP
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\fBversion\fP \(em Display version information.
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.LP
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.SH COMMANDS
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The following commands implement the core LVM functionality.
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.TP
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\fBpvchange\fP \(em Change attributes of a physical volume.
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\fBpvchange\fP \(em Change attributes of a Physical Volume.
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.TP
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\fBpvck\fP \(em Check physical volume metadata.
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\fBpvck\fP \(em Check Physical Volume metadata.
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.TP
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\fBpvcreate\fP \(em Initialize a disk or partition for use by LVM.
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.TP
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\fBpvdisplay\fP \(em Display attributes of a physical volume.
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\fBpvdisplay\fP \(em Display attributes of a Physical Volume.
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.TP
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\fBpvmove\fP \(em Move physical extents.
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\fBpvmove\fP \(em Move Physical Extents.
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.TP
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\fBpvremove\fP \(em Remove a physical volume.
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\fBpvremove\fP \(em Remove a Physical Volume.
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.TP
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\fBpvresize\fP \(em Resize a disk or partition in use by LVM2.
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.TP
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\fBpvs\fP \(em Report information about physical volumes.
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\fBpvs\fP \(em Report information about Physical Volumes.
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.TP
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\fBpvscan\fP \(em Scan all disks for physical volumes.
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\fBpvscan\fP \(em Scan all disks for Physical Volumes.
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.TP
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\fBvgcfgbackup\fP \(em Backup volume group descriptor area.
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\fBvgcfgbackup\fP \(em Backup Volume Group descriptor area.
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.TP
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\fBvgcfgrestore\fP \(em Restore volume group descriptor area.
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\fBvgcfgrestore\fP \(em Restore Volume Group descriptor area.
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.TP
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\fBvgchange\fP \(em Change attributes of a volume group.
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\fBvgchange\fP \(em Change attributes of a Volume Group.
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.TP
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\fBvgck\fP \(em Check volume group metadata.
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\fBvgck\fP \(em Check Volume Group metadata.
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.TP
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\fBvgconvert\fP \(em Convert volume group metadata format.
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\fBvgconvert\fP \(em Convert Volume Group metadata format.
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.TP
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\fBvgcreate\fP \(em Create a volume group.
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\fBvgcreate\fP \(em Create a Volume Group.
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.TP
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\fBvgdisplay\fP \(em Display attributes of volume groups.
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\fBvgdisplay\fP \(em Display attributes of Volume Groups.
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.TP
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\fBvgexport\fP \(em Make volume groups unknown to the system.
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\fBvgexport\fP \(em Make volume Groups unknown to the system.
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.TP
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\fBvgextend\fP \(em Add physical volumes to a volume group.
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\fBvgextend\fP \(em Add Physical Volumes to a Volume Group.
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.TP
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\fBvgimport\fP \(em Make exported volume groups known to the system.
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\fBvgimport\fP \(em Make exported Volume Groups known to the system.
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.TP
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\fBvgimportclone\fP \(em Import and rename duplicated volume group (e.g. a hardware snapshot).
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\fBvgimportclone\fP \(em Import and rename duplicated Volume Group (e.g. a hardware snapshot).
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.TP
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\fBvgmerge\fP \(em Merge two volume groups.
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\fBvgmerge\fP \(em Merge two Volume Groups.
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.TP
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\fBvgmknodes\fP \(em Recreate volume group directory and logical volume special files
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\fBvgmknodes\fP \(em Recreate Volume Group directory and Logical Volume special files
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.TP
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\fBvgreduce\fP \(em Reduce a volume group by removing one or more physical volumes.
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\fBvgreduce\fP \(em Reduce a Volume Group by removing one or more
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Physical Volumes.
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.TP
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\fBvgremove\fP \(em Remove a volume group.
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\fBvgremove\fP \(em Remove a Volume Group.
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.TP
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\fBvgrename\fP \(em Rename a volume group.
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\fBvgrename\fP \(em Rename a Volume Group.
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.TP
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\fBvgs\fP \(em Report information about volume groups.
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\fBvgs\fP \(em Report information about Volume Groups.
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.TP
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\fBvgscan\fP \(em Scan all disks for volume groups and rebuild caches.
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\fBvgscan\fP \(em Scan all disks for Volume Groups and rebuild caches.
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.TP
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\fBvgsplit\fP \(em Split a volume group into two, moving any logical volumes from one volume group to another by moving entire physical volumes.
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\fBvgsplit\fP \(em Split a Volume Group into two, moving any logical
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volumes from one Volume Group to another by moving entire Physical
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Volumes.
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.TP
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\fBlvchange\fP \(em Change attributes of a logical volume.
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\fBlvchange\fP \(em Change attributes of a Logical Volume.
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.TP
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\fBlvconvert\fP \(em Convert a logical volume from linear to mirror or snapshot.
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\fBlvconvert\fP \(em Convert a Logical Volume from linear to mirror or snapshot.
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.TP
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\fBlvcreate\fP \(em Create a logical volume in an existing volume group.
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\fBlvcreate\fP \(em Create a Logical Volume in an existing Volume Group.
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.TP
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\fBlvdisplay\fP \(em Display attributes of a logical volume.
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\fBlvdisplay\fP \(em Display attributes of a Logical Volume.
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.TP
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\fBlvextend\fP \(em Extend the size of a logical volume.
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\fBlvextend\fP \(em Extend the size of a Logical Volume.
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.TP
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\fBlvmchange\fP \(em Change attributes of the logical volume manager.
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\fBlvmchange\fP \(em Change attributes of the Logical Volume Manager.
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.TP
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\fBlvmdiskscan\fP \(em Scan for all devices visible to LVM2.
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.TP
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\fBlvmdump\fP \(em Create lvm2 information dumps for diagnostic purposes.
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.TP
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\fBlvreduce\fP \(em Reduce the size of a logical volume.
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\fBlvreduce\fP \(em Reduce the size of a Logical Volume.
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.TP
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\fBlvremove\fP \(em Remove a logical volume.
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\fBlvremove\fP \(em Remove a Logical Volume.
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.TP
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\fBlvrename\fP \(em Rename a logical volume.
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\fBlvrename\fP \(em Rename a Logical Volume.
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.TP
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\fBlvresize\fP \(em Resize a logical volume.
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\fBlvresize\fP \(em Resize a Logical Volume.
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.TP
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\fBlvs\fP \(em Report information about logical volumes.
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\fBlvs\fP \(em Report information about Logical Volumes.
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.TP
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\fBlvscan\fP \(em Scan (all disks) for logical volumes.
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\fBlvscan\fP \(em Scan (all disks) for Logical Volumes.
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.TP
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The following commands are not implemented in LVM2 but might be in the future: lvmsadc, lvmsar, pvdata.
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.SH OPTIONS
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@ -183,13 +186,13 @@ You are strongly advised not to disable this!
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See \fBvgcfgbackup\fP(8).
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.TP
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.BR \-P ", " \-\-partial
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When set, the tools will do their best to provide access to volume groups
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that are only partially available (one or more physical volumes belonging
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to the volume group are missing from the system). Where part of a logical
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When set, the tools will do their best to provide access to Volume Groups
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that are only partially available (one or more Physical Volumes belonging
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to the Volume Group are missing from the system). Where part of a logical
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volume is missing, \fB/dev/ioerror\fP will be substituted, and you could use
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\fBdmsetup\fP(8) to set this up to return I/O errors when accessed,
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or create it as a large block device of nulls. Metadata may not be
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changed with this option. To insert a replacement physical volume
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changed with this option. To insert a replacement Physical Volume
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of the same or large size use \fBpvcreate \-u\fP to set the uuid to
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match the original followed by \fBvgcfgrestore\fP(8).
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.TP
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@ -239,27 +242,23 @@ The allocation policy to use:
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.IR normal ,
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.IR anywhere " or"
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.IR inherit .
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When a command needs to allocate physical extents from the volume group,
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When a command needs to allocate Physical Extents from the Volume Group,
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the allocation policy controls how they are chosen.
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Each volume group and logical volume has an allocation policy.
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The default for a volume group is \fInormal\fP which applies
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Each Volume Group and Logical Volume has an allocation policy defined.
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The default for a Volume Group is \fInormal\fP which applies
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common-sense rules such as not placing parallel stripes on the same
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physical volume. The default for a logical volume is \fIinherit\fP
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which applies the same policy as for the volume group. These policies can
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be changed using \fBlvchange\fP(8) and \fBvgchange\fP(8) or over-ridden
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Physical Volume. The default for a Logical Volume is \fIinherit\fP
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which applies the same policy as for the Volume Group. These policies can
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be changed using \fBlvchange\fP(8) and \fBvgchange\fP(8) or overridden
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on the command line of any command that performs allocation.
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The \fIcontiguous\fP policy requires that new extents be placed adjacent
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to existing extents.
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The \fIcling\fP policy places new extents on the same physical
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volume as existing extents in the same stripe of the Logical Volume.
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If there are sufficient free extents to satisfy
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The \fIcontiguous\fP policy requires that new Physical Extents be placed adjacent
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to existing Physical Extents.
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The \fIcling\fP policy places new Physical Extents on the same Physical
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Volume as existing Physical Extents in the same stripe of the Logical Volume.
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If there are sufficient free Physical Extents to satisfy
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an allocation request but \fInormal\fP doesn't use them,
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\fIanywhere\fP will - even if that reduces performance by
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placing two stripes on the same physical volume.
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.IP
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N.B. The policies described above are not implemented fully yet.
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In particular, contiguous free space cannot be broken up to
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satisfy allocation attempts.
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placing two stripes on the same Physical Volume.
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.SH ENVIRONMENT VARIABLES
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.TP
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.B HOME
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@ -271,8 +270,8 @@ Directory containing \fBlvm.conf\fP(5) and other LVM system files.
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Defaults to "#DEFAULT_SYS_DIR#".
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.TP
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.B LVM_VG_NAME
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The volume group name that is assumed for
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any reference to a logical volume that doesn't specify a path.
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The Volume Group name that is assumed for
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any reference to a Logical Volume that doesn't specify a path.
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Not set by default.
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.SH VALID NAMES
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The following characters are valid for VG and LV names:
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@ -283,8 +282,77 @@ There are also various reserved names that are used internally by lvm that can n
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A VG cannot be called anything that exists in /dev/ at the time of creation, nor can it be called '.' or '..'.
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A LV cannot be called '.' '..' 'snapshot' or 'pvmove'. The LV name may also not contain
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the strings '_mlog', '_mimage', '_rimage', '_tdata', '_tmeta'.
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.SH ALLOCATION
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When an operation needs to allocate Physical Extents for one or more
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Logical Volumes, the tools proceed as follows:
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First of all, they generate the complete set of unallocated Physical Extents
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in the Volume Group. If any ranges of Physical Extents are supplied at
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the end of the command line, only unallocated Physical Extents within
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those ranges on the specified Physical Volumes are considered.
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Then they try each allocation policy in turn, starting with the strictest
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policy (\fIcontiguous\fP) and ending with the allocation policy specified
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using \fB\-\-alloc\fP or set as the default for the particular Logical
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Volume or Volume Group concerned. For each policy, working from the
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lowest-numbered Logical Extent of the empty Logical Volume space that
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needs to be filled, they allocate as much space as possible according to
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the restrictions imposed by the policy. If more space is needed,
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they move on to the next policy.
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The restrictions are as follows:
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\fIContiguous\fP requires that the physical location of any Logical
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Extent that is not the first Logical Extent of a Logical Volume is
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adjacent to the physical location of the Logical Extent immediately
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preceding it.
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\fICling\fP requires that the Physical Volume used for any Logical
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Extent to be added to an existing Logical Volume is already in use by at
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least one Logical Extent earlier in that Logical Volume. If the
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configuration parameter allocation/cling_tag_list is defined, then two
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Physical Volumes are considered to match if any of the listed tags is
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present on both Physical Volumes. This allows groups of Physical
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Volumes with similar properties (such as their physical location) to be
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tagged and treated as equivalent for allocation purposes.
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When a Logical Volume is striped or mirrored, the above restrictions are
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applied independently to each stripe or mirror image (leg) that needs
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space.
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\fINormal\fP will not choose a Physical Extent that shares the same Physical
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Volume as a Logical Extent already allocated to a parallel Logical
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Volume (i.e. a different stripe or mirror image/leg) at the same offset
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within that parallel Logical Volume.
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When allocating a mirror log at the same time as Logical Volumes to hold
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the mirror data, Normal will first try to select different Physical
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Volumes for the log and the data. If that's not possible and the
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allocation/mirror_logs_require_separate_pvs configuration parameter is
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set to 0, it will then allow the log to share Physical Volume(s) with
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part of the data.
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When allocating thin pool metadata, similar considerations to those of a
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mirror log in the last paragraph apply based on the value of the
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allocation/thin_pool_metadata_require_separate_pvs configuration
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parameter.
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If you rely upon any layout behaviour beyond that documented here, be
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aware that it might change in future versions of the code.
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For example, if you supply on the command line two empty Physical
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Volumes that have an identical number of free Physical Extents available for
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allocation, the current code considers using each of them in the order
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they are listed, but there is no guarantee that future releases will
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maintain that property. If it is important to obtain a specific layout
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for a particular Logical Volume, then you should build it up through a
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sequence of \fBlvcreate\fP(8) and \fBlvconvert\fP(8) steps such that the
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restrictions described above applied to each step leave the tools no
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discretion over the layout.
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To view the way the allocation process currently works in any specific
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case, read the debug logging output, for example by adding \-vvvv to
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a command.
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.SH DIAGNOSTICS
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All tools return a status code of zero on success or non-zero on failure.
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.SH FILES
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