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author | David Teigland <teigland@redhat.com> | 2015-05-01 13:44:31 -0500 |
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committer | David Teigland <teigland@redhat.com> | 2015-05-01 15:23:32 -0500 |
commit | 9273b1a964c4edafbc59598f7a800f5cd524a8f3 (patch) | |
tree | 9438438d30adc10ae68973eb47daf1f11852b172 | |
parent | 9c7063ef893449742922a4bcbcbe6c38f191b8dc (diff) | |
download | lvm2-9273b1a964c4edafbc59598f7a800f5cd524a8f3.tar.gz |
man: expanded explanation of pvscan
Related to it's role with lvmetad and auto-activation.
-rw-r--r-- | man/pvscan.8.in | 146 |
1 files changed, 119 insertions, 27 deletions
diff --git a/man/pvscan.8.in b/man/pvscan.8.in index f976b40e0..010c091c0 100644 --- a/man/pvscan.8.in +++ b/man/pvscan.8.in @@ -1,6 +1,7 @@ .TH PVSCAN 8 "LVM TOOLS #VERSION#" "Sistina Software UK" \" -*- nroff -*- .SH NAME pvscan \(em scan all disks for physical volumes + .SH SYNOPSIS .B pvscan .RB [ \-\-commandprofile @@ -30,9 +31,118 @@ pvscan \(em scan all disks for physical volumes .IR DevicePath | .IR major:minor ]... + .SH DESCRIPTION -pvscan scans all supported LVM block devices in the system for -physical volumes. +pvscan scans all supported LVM block devices in the system for physical +volumes. + +.SS Scanning with lvmetad + +pvscan operates differently when used with the +.BR lvmetad (8) +daemon. + +Scanning disks is required to read LVM metadata and identify LVM PVs. +Once read, lvmetad caches the metadata so that LVM commands can read it +without repeatedly scanning disks. This is helpful because scanning disks +is time consuming, and frequent scanning may interfere with the normal +work of the system and disks. + +When lvmetad is not used, LVM commands revert to scanning disks to read +metadata. Any LVM command that needs metadata will scan disks for it; +running the pvscan command is not necessary for the sake of other LVM +commands. + +When lvmetad is used, LVM commands avoid scanning disks by reading +metadata from lvmetad. When new disks appear, they must be scanned so +their metadata can be cached in lvmetad. This is done by the command +pvscan \-\-cache, which scans disks and passes the metadata to lvmetad. + +The pvscan \-\-cache command is typically run automatically by system +services when a new device appears. Users do not generally need to run +this command if the system and lvmetad are running properly. + +Many scripts contain unnecessary pvscan (or vgscan) commands for +historical reasons. To avoid disrupting the system with extraneous disk +scanning, an ordinary pvscan (without \-\-cache) will simply read metadata +from lvmetad like other LVM commands. It does not do anything beyond +displaying the current state of the cache. + +.I Notes + +.IP \[bu] 2 +When given specific device name arguments, pvscan \-\-cache will only +read the named devices. + +.IP \[bu] 2 +LVM udev rules and systemd services are used to intiate automatic device +scanning. + +.IP \[bu] 2 +To prevent devices from being scanned by pvscan --cache, add them +to +.BR lvm.conf (5) +.B devices/global_filter. +The devices/filter setting does not +apply to system level scanning. +For more information, see: +.br +.B lvmconfig --withcomments devices/global_filter + +.IP \[bu] 2 +If lvmetad is started or restarted after devices are visible, or +if the global_filter has changed, then all devices must be rescanned +for metadata with the command pvscan \-\-cache. + +.IP \[bu] 2 +lvmetad ignores older metadata formats, e.g. lvm1, and should not be +used if they exist. + +.IP \[bu] 2 +To notify lvmetad about a device that is no longer present, the major and +minor numbers must be given, not the path. + +.SS Automatic activation + +When event-driven system services detect a new LVM device, the first step +is to automatically scan and cache the metadata from the device. This is +done by pvscan \-\-cache. A second step is to automatically activate LVs +that are present on the new device. This auto-activation is done by the +same pvscan \-\-cache command when the option '\-a|\-\-activate ay' is +included. + +Auto-activation of VGs or LVs can be enabled/disabled using: +.br +.BR lvm.conf (5) +.B activation/auto_activation_volume_list + +For more information, see: +.br +.B lvmconfig --withcomments activation/auto_activation_volume_list + +When this setting is undefined, all LVs are auto-activated (when lvm is +fully integrated with the event-driven system services.) + +When a VG or LV is not auto-activated, traditional activation using +vgchange or lvchange -a|--activate is needed. + +.I Notes + +.IP \[bu] 2 +pvscan auto-activation can be only done in combination with \-\-cache. + +.IP \[bu] 2 +Auto-activation is designated by the "a" argument in '-a|--activate ay'. +This is meant to distinguish system generated commands from explicit user +commands, although it can be used in any activation command. Whenever it +is used, the auto_activation_volume_list is applied. + +.IP \[bu] 2 +Auto-activation is not yet supported for LVs that are part of partial or +clustered volume groups. + +.P + .SH OPTIONS See \fBlvm\fP(8) for common options. .TP @@ -46,37 +156,19 @@ Only show physical volumes not belonging to any volume group. Short listing format. .TP .BR \-u ", " \-\-uuid -Show UUIDs (Uniform Unique Identifiers) in addition to device special names. +Show UUIDs in addition to device names. .TP .BR \-a ", " \-\-activate " " \fIay -Together with the information already cached in lvmetad, automatically activate -any logical volumes that become activatable after the scan done on one or more devices. -The logical volume to autoactivate is matched against the -activation/auto_activation_volume_list set in lvm.conf. If this list is not set, then -all volumes are considered for autoactivation. The autoactivation is not yet -supported for logical volumes that are part of partial or clustered volume groups. +Automatically activate any logical volumes that are possible to activate +with the addition of the new devices. .TP .BR \-b ", " \-\-background Run the command in the background. .TP .BR \-\-cache " [" \-\-major " " \fImajor " " \-\-minor " " \fIminor " | " \fIDevicePath " | " \fImajor:minor " ]..." -Scan one or more devices and instruct the lvmetad daemon to update its cached -state accordingly. Called internally by udev rules. -All devices listed explicitly are processed \fBregardless\fP of any device -filters set using \fBdevices/filter\fP configuration setting. To filter -devices even in this case, the \fBdevices/global_filter\fP must be used. -If lvmetad has not yet cached any metadata or the filters have recently been -changed, then all devices may be scanned, effectively ignoring the rest of -the command line. Otherwise, if all the devices referenced on the command line -contain metadata in the default lvm2 format, other devices are not accessed. -If metadata written using the obsolete GFS pool or lvm1 format is encountered, -this is ignored and so lvmetad should not be used. -To notify lvmetad about a device that is not present in the system anymore, -\fB\-\-major\fP and \fB\-\-minor\fP pair of that device must be always supplied, -not \fBDevicePath\fP as pvscan is not able to translate the \fBDevicePath\fP -into major and minor pair which lvmetad requires. +Scan one or more devices and send the metadata to lvmetad. + .SH SEE ALSO .BR lvm (8), -.BR lvmetad (8), -.BR pvcreate (8), -.BR pvdisplay (8) +.BR lvmconfig (8), +.BR lvmetad (8) |