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200793edc6
rather than -a|--activate, because web pages on man7.org are not printing the | character.
93 lines
3.7 KiB
Plaintext
93 lines
3.7 KiB
Plaintext
pvscan scans all supported LVM block devices in the system for PVs.
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\fBScanning with lvmetad\fP
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pvscan operates differently when used with the
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.BR lvmetad (8)
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daemon.
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Scanning disks is required to read LVM metadata and identify LVM PVs.
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Once read, lvmetad caches the metadata so that LVM commands can read it
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without repeatedly scanning disks. This is helpful because scanning disks
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is time consuming, and frequent scanning may interfere with the normal
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work of the system and disks.
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When lvmetad is not used, LVM commands revert to scanning disks to read
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metadata. Any LVM command that needs metadata will scan disks for it;
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running the pvscan command is not necessary for the sake of other LVM
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commands.
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When lvmetad is used, LVM commands avoid scanning disks by reading
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metadata from lvmetad. When new disks appear, they must be scanned so
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their metadata can be cached in lvmetad. This is done by the command
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pvscan --cache, which scans disks and passes the metadata to lvmetad.
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The pvscan --cache command is typically run automatically by system
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services when a new device appears. Users do not generally need to run
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this command if the system and lvmetad are running properly.
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Many scripts contain unnecessary pvscan (or vgscan) commands for
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historical reasons. To avoid disrupting the system with extraneous disk
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scanning, an ordinary pvscan (without --cache) will simply read metadata
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from lvmetad like other LVM commands. It does not do anything beyond
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displaying the current state of the cache.
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.IP \[bu] 2
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When given specific device name arguments, pvscan --cache will only
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read the named devices.
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.IP \[bu] 2
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LVM udev rules and systemd services are used to initiate automatic device
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scanning.
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.IP \[bu] 2
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To prevent devices from being scanned by pvscan --cache, add them
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to
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.BR lvm.conf (5)
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.B devices/global_filter.
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The devices/filter setting does not
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apply to system level scanning.
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For more information, see:
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.br
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.B lvmconfig --withcomments devices/global_filter
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.IP \[bu] 2
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If lvmetad is started or restarted after devices are visible, or
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if the global_filter has changed, then all devices must be rescanned
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for metadata with the command pvscan --cache.
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.IP \[bu] 2
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lvmetad does not cache older metadata formats, e.g. lvm1, and will
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be temporarily disabled if they are seen.
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.IP \[bu] 2
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To notify lvmetad about a device that is no longer present, the major and
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minor numbers must be given, not the path.
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.P
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\fBAutomatic activation\fP
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When event-driven system services detect a new LVM device, the first step
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is to automatically scan and cache the metadata from the device. This is
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done by pvscan --cache. A second step is to automatically activate LVs
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that are present on the new device. This auto-activation is done by the
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same pvscan --cache command when the option --activate ay is included.
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Auto-activation of VGs or LVs can be enabled/disabled using:
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.br
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.BR lvm.conf (5)
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.B activation/auto_activation_volume_list
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For more information, see:
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.br
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.B lvmconfig --withcomments activation/auto_activation_volume_list
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When this setting is undefined, all LVs are auto-activated (when lvm is
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fully integrated with the event-driven system services.)
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When a VG or LV is not auto-activated, traditional activation using
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vgchange or lvchange --activate is needed.
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.IP \[bu] 2
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pvscan auto-activation can be only done in combination with --cache.
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.IP \[bu] 2
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Auto-activation is designated by the "a" argument in --activate ay.
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This is meant to distinguish system generated commands from explicit user
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commands, although it can be used in any activation command. Whenever it
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is used, the auto_activation_volume_list is applied.
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.IP \[bu] 2
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Auto-activation is not yet supported for LVs that are part of partial or
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clustered volume groups.
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