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author | David Teigland <teigland@redhat.com> | 2017-01-18 15:08:20 -0600 |
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committer | David Teigland <teigland@redhat.com> | 2017-02-07 10:38:30 -0600 |
commit | d41a2e6f305a9c23d2112eebaeae6600076d883b (patch) | |
tree | 330ca474c890171f0149e3f7598af2d0e08da5af | |
parent | 55d6e9ebb7e78692fdabbff2a5400ad2d6987ede (diff) | |
download | lvm2-d41a2e6f305a9c23d2112eebaeae6600076d883b.tar.gz |
man: add pvscan notes
from previous man page
-rw-r--r-- | man/pvscan.8.notes | 103 |
1 files changed, 103 insertions, 0 deletions
diff --git a/man/pvscan.8.notes b/man/pvscan.8.notes new file mode 100644 index 000000000..6dc505c85 --- /dev/null +++ b/man/pvscan.8.notes @@ -0,0 +1,103 @@ +.SH NOTES + +.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. + +.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 initiate 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 does not cache older metadata formats, e.g. lvm1, and will +be temporarily disabled if they are seen. + +.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. + +.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. + |